Process for the preparation of flocculated filler particles

ABSTRACT

The present invention concerns a process for the preparation of flocculated filler particles, wherein at least two aqueous suspensions of at least one filler material and at least one flocculating additive are combined.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. national phase of PCT Application No. PCT/EP2015/074472,filed Oct. 22, 2015, which claims priority to European Application No.14192379.7, filed Nov. 7, 2014 and U.S. Provisional Application No.62/079,662, filed Nov. 14, 2014.

The present invention relates to a process for the preparation offlocculated filler particles, flocculated filler particles obtained fromsaid process and their use as well as to products containing saidflocculated filler particles.

Mineral materials and binders are among the main constituents used inthe manufacture of numerous products such as paints, paper and plasticmaterials. Therein, mineral materials contribute to mechanical andoptical properties, while the binders, generally latex-based and in theform of aqueous suspensions or dispersions, provide the necessaryadhesion and cohesion for the respective constituents of the end productto be produced.

In order to avoid the logistic difficulties of handling mineralmaterials and binders separately, and further to avoid the unwantedphysical and chemical interactions developed in comparable mixtures ofmineral materials and binders, self-binding pigment particles have beendeveloped and are known to industry. In this regard, self-bindingpigment particles having both the properties of the mineral material andof the binder may be directly implemented in a variety of applications.This unique product named self-binding pigment particles refers todistinct, solid particles, formed of mineral material and binder thatare intimately bound to one another. The internal cohesion forces aresuch as to provide the self-binding pigment particles with excellentmechanical stability.

Self-binding pigment particles can be produced from calcium carbonatecontaining mineral materials, for example, from natural mineral pigmentmaterials which are commonly prepared by a process implementing at leastone step of grinding mineral materials in the presence of binder.Grinding refers to an operation leading to a reduction in the particlesize, i.e. the mineral materials in the self-binding pigment particleshave a smaller diameter than the initial mineral material used toproduce them. Such self-binding pigment particles are described in anumber of documents, including WO 2006/008657, WO 2006/128814, and WO2008/139292. Processes for preparing self-binding pigment particles arealso known from EP 2 505 614 A1, EP 2 505 615 A1, EP 2 565 237 A1, EP 2565 236 A1, EP 2 662 416 A1, EP 2 379 649 A1, EP 2 662 417 A1, and EP 2662 419 A1. EP 1 747 252 A1 relates to a method for producingsurface-modified inorganic fillers.

The processes for preparing self-binding mineral pigment particles knownin the art are often limited to the preparation or the co-grinding ofsuspensions having a low solids content. However, the preparation of lowsolids content suspensions has the disadvantage that the obtained groundproduct has to be concentrated before being shipped to other facilitiesfor further processing. During the time and energy consumingconcentrating step, very often an undesired loss of polymeric binder isobserved, and, additionally, unwanted agglomerates are formed.Furthermore, the prior art processes often lead to a suspension having ahigh total organic content of the aqueous phase of the groundsuspension. Moreover, the addition of dispersant, however, inter aliaaffects the adsorption of the binder to the particles duringco-grinding.

A further problem, which very often has significant impact on themechanical and optical properties of papers and paper coatings made fromsuch self-binding pigment particles, is encountered in respect to thebinding between the fibres and such self-binding pigment particles. Theself-binding pigment particle suspensions often diminish the mechanicaland optical properties of the corresponding end products. One reason forthis may be the shape of the self-binding pigment particles, which couldhamper the interaction between the self-binding pigment particles andthe fibres of the paper. Thus, to produce paper articles withwell-adjusted mechanical and optical properties, the interactionboundaries between the self-binding pigment particles and the fibres inthe paper have to be optimized.

Furthermore, high filler levels in paper are desirable since these wouldprovide the possibility to reduce the amount of wood fibres in thepaper. Moreover, papers with high filler content will dry faster, and,as a result, the paper machine can run faster. Consequently, theaddition of high levels of filler can reduce paper production costs andcan save natural resources. However, such high filler levels oftenreduce the area of contact between the remaining fibres. As a result,retaining high amounts of filler with a suboptimal shape produces aweaker sheet that can break more easily on the paper machines, sizepresses, coaters, winders, printing presses, printing machines, or copymachines.

U.S. Pat. No. 5,611,890 A relates to a strong, soft filled tissue papercomprising a non-cellulosic particulate filler, wherein said fillercomprises 5 to 50 wt.-% of said tissue paper. WO 03/087472 A1 disclosesa filler treatment comprising the preparation of swollen starch-latexcompositions, and the addition of said compositions to a fillersuspension. The use of these treated fillers during papermaking improvesfiller retention and produces filled papers, where addition of thefiller has only a minimal negative effect on strength properties. Apapermaking filler material which has been surface treated with acationic polymer is described in CA 2,037,525 A1. The article“Improvement of paper properties using starch-modified precipitatedcalcium carbonate filler” of Zhao et al., TAPPI Journal 2005, vol. 4(2),is concerned with commercial precipitated calcium carbonate fillers thathave been modified with corn and potato raw starches. These modifiedfillers were used as papermaking fillers to improve the strength in highfiller content papers.

It has also been proposed to utilize pre-flocculated filler compositionsin papermaking. In such pre-flocculated filler compositions the filleris accompanied in aqueous suspension by a flocculant which modifies thecondition and in some cases the effective particle size of the filler.Such compositions may have an enhanced ability to flocculate onto thepaper fibres, enabling higher filler loadings in paper while maintaininggood strength and optical properties. Methods of preparing stabledispersions of flocculated filler particles for use in papermakingprocesses are described in WO 2014/070488 A1, WO 2013/158811 A1, WO2010/126712 A1 and WO 2009/036271 A1. WO 2013/107933 A1 relates to amethod for producing paper involving the use of a pre-treated fillerdispersion comprising flocs.

In view of the foregoing, improving the self-binding pigment particleproduction process remains of interest to the skilled man.

Accordingly, it is an object of the present invention to provide fillerparticles, which are self-binding, and thus, do not require the presenceof a binder during paper production processes. It would be desirable toprovide self-binding filler particles that improve the binding betweenthe fibres in papers and paper coatings and the self-binding fillerparticles, and, thus, allows for the production of paper articles orfleece materials with well-adjusted mechanical and optical properties.In particular, it is desirable, to provide filler particles that show agood retention in paper production processes, and avoid the use of largeamounts of retention aids.

It would be especially desirable to provide a process for making suchfiller particles, wherein the mineral pigment particles do not have tobe co-ground with the binder since milling is a very cost- andtime-consuming step. Furthermore, the particle structure of the fillerparticles can change during milling and, therefore, the characteristicsof the mineral pigment particles may be different after milling.Moreover, it is desirable to provide a process for the manufacturing ofspecific filler particles allowing control of certain properties of thepaper, e.g. brightness, opacity, air permeability, bulk, printability,or mechanical properties.

The foregoing and other objectives are solved by the subject-matter asdefined herein in the independent claims.

According to one aspect of the present invention, a process for thepreparation of flocculated filler particles is provided, comprising thesteps of

-   -   a) providing at least two aqueous suspensions each comprising at        least one filler material, characterized in that        -   i) a first aqueous suspension S1 comprises at least one            flocculating additive A, and        -   ii) a second aqueous suspension S2 comprises at least one            flocculating additive B which is different from flocculating            additive A, and        -   iii) the at least one filler material in the first aqueous            suspension S1 and the second aqueous suspension S2 is            different, and    -   b) combining the at least two aqueous suspensions provided in        step a) by bringing them together to form an aqueous suspension        SM of flocculated filler particles, wherein the mass ratio of        the at least one filler material in the first aqueous suspension        and the second aqueous suspension S1:S2 is from 1:100 to 100:1.

According to another aspect of the present invention, a process for thepreparation of a fleece comprising steps a) and b) of the processaccording to the present invention is provided, characterized in thatthe aqueous suspension SM of flocculated filler particles obtained afterprocess step b) is combined in a further step c) with synthetic and/ornatural fibres, and the resulting suspension SMF is subjected to adewatering step d) to obtain a fleece.

According to still another aspect of the present invention, aflocculated filler particle suspension obtained by a process accordingto the present invention is provided, characterized in that the fillerparticles have a mono-modal particle size distribution and/or a volumedefined particle size polydispersity expressed as full width at halfmaximum height (FWHM) of less than 45 μm and/or a volume determinedmedian particle size (d₅₀) in the range from 5 to 50 μm.

According to still another aspect of the present invention, aflocculated filler particle suspension is provided, characterized inthat the filler particles have a mono-modal particle size distributionand/or a volume defined particle size polydispersity expressed as fullwidth at half maximum height (FWHM) of less than 45 μm and/or have avolume determined median particle size (d₅₀) in the range from 5 to 50μm.

According to still another aspect of the present invention, a fleece,preferably a sheet of paper, obtained by a process according to thepresent invention is provided.

According to still another aspect of the present invention, a use of aflocculated filler particle suspension according to the presentinvention in paper coating and/or paper wet end applications, preferablyin high filler load paper wet end applications, or for cigarette paperis provided.

Advantageous embodiments of the present invention are defined in thecorresponding sub-claims.

According to one embodiment step b) is carried out by bringing the firstaqueous suspension S1 and the second aqueous suspension S2simultaneously together.

According to another embodiment the Brookfield viscosity of the firstaqueous suspension S1 and/or the second aqueous suspension S2 and/or theaqueous suspension SM is less than 5 000 mPa·s at 25° C., preferablyless than 1 000 mPa·s at 25° C., and more preferably between 10 and 200mPa·s at 25° C.

According to one embodiment the at least one flocculating additive A isa cationic polymer selected from the group consisting of cationicstarch, polyamines, polyethyleneimines, polyacrylamides, cationic amineamide, epichlorohydrin resins, polydiallyldimethylammonium chloride,cationic guar and/or mixtures thereof, preferably the at least oneflocculating additive A is cationic starch. According to anotherembodiment the at least one flocculating additive B is an anionicpolymer selected from the group consisting of carboxymethyl cellulose,anionic starch, anionic guar, anionic xanthan gum and/or mixturesthereof, preferably the at least one flocculating additive B is anioniccarboxymethyl cellulose.

According to one embodiment the aqueous suspension SM is sheared duringand/or after process step b), preferably in at least two steps atdifferent shear rates, and more preferably in at least two steps atdifferent shear rates, wherein the first shear rate is lower than thesecond shear rate. According to another embodiment the at least onefiller material is selected from the group consisting of a calciumcarbonate-comprising material like ground calcium carbonate,precipitated calcium carbonate, modified calcium carbonate, talc, clay,dolomite, marble, titanium dioxide, kaolin, silica, alumina, mica,aluminium trihydrate, magnesium hydroxide, plastic pigments, a hybridmaterial comprising an organic filler and an inorganic chemicalcomposition and mixtures thereof, preferably the at least one fillermaterial is precipitated calcium carbonate.

According to one embodiment the at least one filler material in thefirst aqueous suspension S1 and the at least one filler material in thesecond aqueous suspension S2 is different and the at least one fillermaterial is selected from the group consisting of a calciumcarbonate-comprising material like ground calcium carbonate,precipitated calcium carbonate, modified calcium carbonate, talc, clay,dolomite, marble, titanium dioxide, kaolin, silica, alumina, mica,aluminium trihydrate, magnesium hydroxide, plastic pigments, andmixtures thereof, preferably the filler material in the first suspensionS1 is ground calcium carbonate and the filler material in the secondsuspension S2 is selected from precipitated calcium carbonate and/orclay.

According to one embodiment the content of the at least one flocculatingadditive A in the first aqueous suspension S1 is from 0.001 to 20 wt.-%,more preferably from 0.5 to 10 wt.-%, and most preferably from 3 to 5wt.-%, based on the total weight of the first aqueous suspension S1,and/or the content of the at least one flocculating additive B in thesecond aqueous suspension S2 is from 0.001 to 20 wt.-%, more preferablyfrom 0.1 to 10 wt.-%, and most preferably from 0.2 to 0.8 wt.-%, basedon the total weight of the second aqueous suspension S2. According toanother embodiment the content of the at least one filler material inthe first aqueous suspension S1 is from 1 to 85 wt.-%, preferably from15 to 65 wt.-%, and most preferably from 10 to 40 wt.-%, based on thetotal weight of the first aqueous suspension S1, and the content of theat least one filler material in the second aqueous suspension S2 is from1 to 85 wt.-%, preferably from 15 to 65 wt.-%, and most preferably from10 to 40 wt.-%, based on the total weight of the second aqueoussuspension S2.

According to one embodiment the mass ratio of the at least one fillermaterial in the first aqueous suspension and the second aqueoussuspension S1:S2 is between 99:1 and 1:99, preferably between 95:15, and5:85 most preferably between 70:30 and 30:70. According to anotherembodiment the solids content of the aqueous suspension SM obtainedafter process step b) is from 1 to 75 wt.-%, preferably from 2 to 60wt.-%, and most preferably from 5 to 35 wt.-%, based on the total weightof the aqueous suspension SM.

According to one embodiment the dewatering step d) is carried out on ascreen, preferably via a head box of a paper machine.

It should be understood that for the purpose of the present invention,the following terms have the following meaning:

A “suspension” or “slurry” in the meaning of the present inventioncomprises insoluble solids and a solvent or liquid, preferably water,and optionally further additives, and usually contains large amounts ofsolids and, thus, is more viscous and can be of higher density than theliquid from which it is formed.

A “filler material” in the meaning of the present invention can be anatural or synthetic pigment or a mineral material. Moreover, the fillermaterial can be a hybrid material comprising an organic filler and aninorganic chemical composition. These compounds are inter alia describedin EP 1 773 950 A2.

For the purpose of the present invention, a “mineral material” is asolid substance having a definite inorganic chemical composition andcharacteristic crystalline and/or amorphous structure. For example, amineral material may encompass calcium carbonate such as calcite,aragonite, marble, limestone and chalk, talc, dolomite, mica, titaniumdioxide, aluminium trihydrate such as gibbsite, bayerite, magnesiumhydroxide such as brucite, hydromagnesite, and mixtures thereof.

A “calcium carbonate comprising material” in the meaning of the presentinvention can be a mineral material or a synthetic material having acontent of calcium carbonate of at least 50 wt.-%, preferably 75 wt.-%,more preferably 90 wt.-%, and most preferably 95 wt.-%, based on thetotal weight of the calcium carbonate containing material.

“Ground calcium carbonate” (GCC) in the meaning of the present inventionis a calcium carbonate obtained from natural sources, such as limestone,marble, or chalk, and processed through a wet and/or dry treatment suchas grinding, screening and/or fractionation, for example by a cyclone orclassifier.

“Precipitated calcium carbonate” (PCC) in the meaning of the presentinvention is a synthesized material, generally obtained by precipitationfollowing a reaction of carbon dioxide and calcium hydroxide (hydratedlime) in an aqueous environment or by precipitation of a calcium and acarbonate source in water. Additionally, precipitated calcium carbonatecan also be the product of introducing calcium and carbonate salts,calcium chloride and sodium carbonate for example, in an aqueousenvironment.

“Modified calcium carbonate” (MCC) in the meaning of the presentinvention may feature a natural ground or precipitated calcium carbonatewith an internal structure modification or a surface-reaction product,i.e. “surface-reacted calcium carbonate”. A “surface-reacted calciumcarbonate” is a material comprising calcium carbonate and insoluble,preferably at least partially crystalline, calcium salts of anions ofacids on the surface. Preferably, the insoluble calcium salt extendsfrom the surface of at least a part of the calcium carbonate. Thecalcium ions forming said at least partially crystalline calcium salt ofsaid anion originate largely from the starting calcium carbonatematerial. MCCs are described, for example, in US 2012/0031576 A1, WO2009/074492 A1, EP 2 264 109 A1, EP 2 070 991 A1, or 2 264 108 A1.

Throughout the present document, the “particle size” of a fillermaterial or other particulate material is described by its distributionof particle sizes. The value d_(x) represents the diameter relative towhich x % by volume of the particles have diameters less than d_(x). Thed₅₀ value is thus the volume determined medium particle size, i.e. 50%of the total volume of all particles results from particles bigger and50% of the total volume of all particles results from particles smallerthan this particle size. For the purpose of the present invention theparticle size is specified as volume determined particle size d₅₀ unlessindicated otherwise. For determining the volume determined mediumparticle size d₅₀ a Mastersizer 2000 or Mastersizer 3000 from thecompany Malvern Instruments Ltd., Great Britain, using the Fraunhoferlight scattering model. The weight determined particle size distributionmay correspond to the volume determined particle size if the density ofall the particles is equal.

The term “mono-modal particle size distribution” as used herein refersto a collection of particles which have a single clearly discerniblemaximum on a particle size distribution curve (frequency on the ordinateor y-axis, and particle size on the abscissa or x-axis).

In other words, less than 10%, of the area under a particle sizedistribution curve occurs outside the distribution defined around asingle peak.

The term “volume defined particle size polydispersity” is to beunderstood as a characteristic describing the breadth of distribution ofparticle size to be found amongst the pigment particles. For the purposeof the present invention the volume defined particle size polydispersityis expressed as full width at half maximum of the single particle sizedistribution peak. In case the particle size distribution is notmono-modal, the full width at half maximum relates to the main particlesize distribution peak, i.e. the peak of the particle size distributionhaving the largest area under the curve. A “full width at half maximum(FWHM)” is an expression of the extent of a function, given by thedifference between the two extreme values of the independent variable atwhich the dependent variable is equal to half of its maximum value. Thetechnical term full width at half maximum, or FWHM, is used toapproximate the diameter distribution of the majority of the particles,i.e. the polydispersity of the particle sizes.

In the gist of present invention a “flocculating additive” is a compoundwhich can promote flocculation by causing suspended filler particles toform aggregates called flocs. The flocculating additive may causeflocculation in combination with another additive, preferably anotherflocculating additive, and/or with the filler material alone. In casethat the flocculation occurs with the filler material alone, thisflocculation can be distinguished from the flocculation occurring aftercombining step b) of the process of the present invention. For example,the flocs which form after the process step b) may have a differentparticles size than the flocs generated from one flocculating agent andthe mineral filler alone.

As used herein the term “polymer” generally includes homopolymers andco-polymers such as, for example, block, graft, random and alternatingcopolymers, as well as blends and modifications thereof.

The term “anionic polymer” in the meaning of the present inventionrefers to a polymer having a negative net charge. Said compound istypically modified with anionic groups. The term “anionic” does notexclude the presence of cationic groups provided that the sum ofindividual charges is negative. The term “cationic polymer” in themeaning of the present invention refers to a polymer having a netpositive charge. Said compound is typically modified with cationicgroups. The term “cationic” does not exclude the presence of anionicgroups provided that the sum of individual charges is positive.

The term “positive charges” is to be understood hereinafter to mean thatthe particles have a positive zeta potential at their surface (cf. P.Ney “Zeta potentials and floatability of minerals”, Applied Mineralogy6, Springer Publications, Vienna, N.Y., 1973, especially page 22 etseq.). This applies analogously to the “negative charges” as occur forexample in cellulose fibre and anionically stabilized suspensions. Forthe neutral “charges”, with respect to the particles, towards theoutside the negative and positive charges cancel each other out. Theisoelectric point need not lie at pH=7. The isoelectric point ofparticle surfaces and amphoteric polyelectrolytes and/or their salts,partial salts and/or full salts lies at the pH value at which thepositive and negative charges neutralize each other mutually towards theoutside.

Within the framework of the invention, “neutral monomer units” meanmonomer units which do not contain any dissociable groups (for examplethe —COOH group), e.g. ethylene groups.

The externally, i.e. towards the outside, charged and externally neutralpolymers are defined in the present application by the number of thepositive or negative groups in the polymer. Accordingly, in theamphoteric externally neutral polymers the number of the positivecharges in the cationic monomer units is equal to the number of thenegative charges in the anionic monomer units. In the amphotericcationic polymers the non-neutral monomer units carry predominantlypositive charges. In the amphoteric anionic polymers the non-neutralmonomer units carry predominantly negative charges. This does nothowever mean that for example with an excess of positive charges thepolymers is automatically electrically positive. This is because the“acid strength” and the “base strength” may each be different. Thus, forexample, an amphoteric polymer having an equal number of positive andnegative groups may be electrically either positive or negative orneutral. This applies correspondingly also to the amphoteric cationicpolymers and the amphoteric anionic polymers. By changing the pH valuethe dissociation of the “acid or base groups” can be influenced. Theneutralization of the negative groups with mono and/or bi and/ortrivalent cations also influences their dissociation degree and thus thecharge state towards the outside.

The term “intrinsic viscosity” as used in the context of the presentinvention is a measure of the capability of a polymer in solution toenhance the viscosity of the solution and is specified in ml/g.

Throughout the present document, the “degree of carboxylation” isspecified in respect to the total amount of hydroxyl groups perunmodified monomer unit of the original polysaccharide. A “degree ofcarboxylation” of 1 means that one of the three hydroxyl groups of theunmodified monomer unit of the original polysaccharide is carboxylated.

As used in the context of the present invention, the term “fleece”refers to a flat material produced by pressing together moist fibres,and drying them into flexible sheets. The fibres can be synthetic ornatural fibres. Examples of a fleece are paper-like materials such aspaper, cardboard, or containerboard.

A “specific BET surface area” (SSA) in the meaning of the presentinvention is defined as the surface area of the filler materialparticles divided by the mass of said particles. As used therein thespecific surface area is measured by adsorption using the BET isotherm(ISO 9277:1995) and is specified in m²/g.

For the purpose of the present invention, the “solids content” of aliquid composition is a measure of the amount of material remainingafter all the solvent or water has been evaporated.

For the purpose of the present invention, the term “viscosity” or“Brookfield viscosity” refers to Brookfield viscosity. The Brookfieldviscosity is for this purpose measured by a Brookfield (Type RVT)viscometer at 25° C.±1° C. at 100 rpm using an appropriate spindle ofthe Brookfield RV-spindle set and is specified in mPa·s. Based on histechnical knowledge, the skilled person will select a spindle from theBrookfield RV-spindle set which is suitable for the viscosity range tobe measured. For example, for a viscosity range between 200 and 800mPa·s the spindle number 3 may be used, for a viscosity range between400 and 1 600 mPa·s the spindle number 4 may be used, and for aviscosity range between 800 and 3 200 mPa·s the spindle number 5 may beused.

The term “dry” filler material is understood to be a filler materialhaving less than 0.3% by weight of water relative to the filler materialweight. The % water (equal to “residual total moisture content”) isdetermined according to the Coulometric Karl Fischer measurement method,wherein the filler material is heated to 220° C., and the water contentreleased as vapour and isolated using a stream of nitrogen gas (at 100ml/min) is determined in a Coulometric Karl Fischer unit.

For the purpose of the present invention, the term “shear rate” refersthe rate at which a progressive shearing deformation is applied to amaterial. Throughout the present invention, the shear rate for a fluidbetween two surfaces that occurs by the relative movement between thetwo surfaces in the present invention is defined according to:

${\text{·}\overset{.}{\gamma}} = \frac{v}{h}$whereas{dot over (γ)} is the shear rate in (1/s),v is the relative velocity between the two surfaces in (m/s), andh is the distance between the two surfaces in (m). In case of a stirrer,h corresponds to the distance between the outermost circumference of thestirrer and the inner diameter of the vessel.

Alternatively, the shear rate for a fluid in a pipe in the presentinvention is defined as:

$\overset{.}{\gamma} = \frac{4\; Q}{\pi\; r^{3}}$whereas{dot over (γ)} is the shear rate in (1/s),Q is the volumetric flow of the fluid in (m³/s), andr is the inner pipe radius in (m).

For the sake of simplicity, the fluid is considered to be Newtonian inthese calculations and turbulent flow is not considered. However, if amore accurate calculation of the shear rates is needed, models aspresented e.g. by Jie Wu et al., AIChE Journal, July 2006, Vol. 52, No.7, 2323-2332, can also be applied.

Where the term “comprising” is used in the present description andclaims, it does not exclude other elements. For the purposes of thepresent invention, the term “consisting of” is considered to be apreferred embodiment of the term “comprising of”. If hereinafter a groupis defined to comprise at least a certain number of embodiments, this isalso to be understood to disclose a group, which preferably consistsonly of these embodiments.

Where an indefinite or definite article is used when referring to asingular noun, e.g. “a”, “an” or “the”, this includes a plural of thatnoun unless something else is specifically stated.

Terms like “obtainable” or “definable” and “obtained” or “defined” areused interchangeably. This, for example, means that, unless the contextclearly dictates otherwise, the term “obtained” does not mean toindicate that, for example, an embodiment must be obtained by, forexample, the sequence of steps following the term “obtained” even thoughsuch a limited understanding is always included by the terms “obtained”or “defined” as a preferred embodiment.

The inventive process for the preparation of flocculated fillerparticles comprises the steps of (a) providing at least two aqueoussuspensions each comprising at least one filler material, and (b)combining the at least two aqueous suspensions provided in step (a) bybringing them together to form an aqueous suspension SM of flocculatedfiller particles, wherein the mass ratio of the at least one fillermaterial in the first aqueous suspension and the second aqueoussuspension S1:S2 is from 1:100 to 100:1. The at least two aqueoussuspensions provided in step (a) are characterized in that (i) a firstaqueous suspension S1 comprises at least one flocculating additive A,and (ii) a second aqueous suspension S2 comprises at least oneflocculating additive B which is different from flocculating additive A,and (iii) the at least one filler material in the first aqueoussuspension S1 and the second aqueous suspension S2 is different. The pHvalue of both aqueous suspensions S1 and S2 may be the same or differentand can be adjusted by the addition of Brønstedt acids or bases.Moreover, the charge of the filler particles in the aqueous suspensionsS1 and S2 may be the same or different.

In the following the details and preferred embodiments of the inventiveprocess will be set out in more detail. It is to be understood thatthese technical details and embodiments also apply to the inventiveflocculated filler particle suspensions, their use, and productscontaining the same.

The Filler Material

According to step a) of the process of the present invention at leasttwo aqueous suspensions are provided each comprising at least one fillermaterial.

The term “aqueous” suspension refers to a system, wherein the liquidphase or solvent of the suspension comprises, preferably consists of,water. However, said term does not exclude that the aqueous suspensioncomprises an organic solvent selected from the group comprising alcoholssuch as methanol, ethanol, isopropanol, carbonyl-group containingsolvents such as ketones, e.g. acetone or aldehydes, esters such asisopropyl acetate, carboxylic acids such as formic acid, sulphoxidessuch as dimethyl sulphoxide, and mixtures thereof. If the aqueoussuspension comprises an organic solvent, the aqueous suspensioncomprises the organic solvent in an amount up to 40.0 wt.-% preferablyfrom 1.0 to 30.0 wt.-% and most preferably from 1.0 to 25.0 wt.-%, basedon the total weight of the liquid phase of the aqueous suspension. Forexample, the liquid phase of the aqueous suspension consists of water.If the liquid phase of the aqueous suspension consists of water, thewater to be used can be any water available such as tap water and/ordeionised water.

The term “at least two” aqueous suspensions in the meaning of thepresent invention means that two or more aqueous suspensions areprovided in step a).

In one embodiment of the present invention, two aqueous suspensions areprovided in step a). Alternatively, three or more aqueous suspensionsare provided in step a). For example, two or three aqueous suspensionsare provided in step a). Preferably, two aqueous suspensions areprovided in step a).

Thus, at least a first aqueous suspension S1 and a second aqueoussuspension S2 are provided in step a).

According to one embodiment of the present invention, the aqueoussuspensions are obtained by mixing particles of the at least one fillermaterial with a solvent, preferably water. The at least one fillermaterial to be mixed with a solvent, and preferably water, may beprovided in any form, for example, as suspension, slurry, dispersion,paste, powder, a moist filter cake or in pressed or granulated form. Ina preferred embodiment the at least one filler material is provided inform of a powder. In another preferred embodiment the at least onefiller material is provided in form of a slurry, and more preferably inform of an aqueous slurry. Said slurry may have a solids content from 1to 85 wt.-%, even more preferably from 10 to 75 wt.-%, and mostpreferably from 15 to 65 wt.-%, based on the total weight of the slurry.

According to one embodiment the content of the at least one fillermaterial in the first aqueous suspension S1 is from 1 to 85 wt.-%,preferably from 15 to 65 wt.-%, and most preferably from 10 to 40 wt.-%,based on the total weight of the first aqueous suspension S1, and thecontent of the at least one filler material in the second aqueoussuspension S2 is from 1 to 85 wt.-%, preferably from 15 to 65 wt.-%, andmost preferably from 10 to 40 wt.-%, based on the total weight of thesecond aqueous suspension S2.

The solids content of the aqueous suspensions can be adjusted by themethods known to the skilled person. To adjust the solids content of anaqueous suspension, the aqueous suspension may be partially dewatered bya settling, filtration, centrifugation or thermal separation process.For example, the first aqueous suspension S1 of the at least two aqueoussuspensions provided in step a) is obtained by partially dewatering anaqueous suspension by centrifugation to the desired solids contentand/or the second aqueous suspension S2 of the at least two aqueoussuspensions provided in step a) is obtained by partially dewatering thesupernatant separated from the first aqueous suspension by settling tothe desired solids content. The partial dewatering by centrifugationand/or settling can be carried out by using methods well known to theskilled person.

It is a requirement of the process of the present invention that themass ratio of the at least one filler material in the first aqueoussuspension and the second aqueous suspension S1:S2 is from 1:100 to100:1.

According to one embodiment, the mass ratio of the at least one fillermaterial in the first aqueous suspension and the second aqueoussuspension S1:S2 is between 99:1 and 1:99, preferably between 95:15, and5:85 most preferably between 70:30 and 30:70. According to anotherembodiment, the mass ratio of the at least one filler material in thefirst aqueous suspension and the second aqueous suspension S1:S2 is from1:75 to 75:1, preferably from 1:50 to 50:1, more preferably from 1:25 to25:1, even more preferably from 1:10 to 10:1, and most preferably from1:5 to 5:1. The mass ratio is based on the dry weight of the at leastone filler material.

According to one embodiment of the present invention, the fillermaterial is a natural or synthetic pigment or mineral material.According to another embodiment, the filler material can be a hybridmaterial comprising an organic filler, e.g. starch, and an inorganicchemical composition, e.g., a mineral material. Hybrid materials areinter alia described in EP 1 773 950 A2.

The at least one filler material may be selected from the groupconsisting of a calcium carbonate-comprising material, a mixed carbonatebased filler, talc, clay, dolomite, marble, titanium dioxide, kaolin,silica, alumina, mica, aluminium trihydrate, magnesium hydroxide,plastic pigments, and mixtures thereof.

According to one embodiment, the at least one filler material is acalcium carbonate-comprising material, preferably selected from thegroup consisting of ground calcium carbonate, precipitated calciumcarbonate, modified calcium carbonate, and mixtures thereof. Accordingto a preferred embodiment the at least one filler material isprecipitated calcium carbonate.

Ground (or natural) calcium carbonate (GCC) is understood to bemanufactured from a naturally occurring form of calcium carbonate, minedfrom sedimentary rocks such as limestone or chalk, or from metamorphicmarble rocks, eggshells or seashells. Calcium carbonate is known toexist as three types of crystal polymorphs: calcite, aragonite andvaterite. Calcite, the most common crystal polymorph, is considered tobe the most stable crystal form of calcium carbonate. Less common isaragonite, which has a discrete or clustered needle orthorhombic crystalstructure. Vaterite is the rarest calcium carbonate polymorph and isgenerally unstable. Ground calcium carbonate is almost exclusively ofthe calcitic polymorph, which is said to be trigonal-rhombohedral andrepresents the most stable of the calcium carbonate polymorphs. The term“source” of the calcium carbonate in the meaning of the presentapplication refers to the naturally occurring mineral material fromwhich the calcium carbonate is obtained. The source of the calciumcarbonate may comprise further naturally occurring components such asmagnesium carbonate, alumino silicate etc.

According to one embodiment of the present invention the source ofground calcium carbonate (GCC) is selected from marble, chalk, dolomite,limestone, or mixtures thereof. Preferably, the source of ground calciumcarbonate is selected from marble. According to one embodiment of thepresent invention the GCC is obtained by dry grinding. According toanother embodiment of the present invention the GCC is obtained by wetgrinding and subsequent drying.

“Dolomite” in the meaning of the present invention is a carboniccalcium-magnesium-mineral having the chemical composition of CaMg(CO₃)₂(“CaCO₃.MgCO₃”). A dolomite mineral may contain at least 30.0 wt.-%MgCO₃, based on the total weight of dolomite, preferably more than 35.0wt.-%, and more preferably more than 40.0 wt.-% MgCO₃.

According to one embodiment of the present invention, the calciumcarbonate-comprising material comprises one ground calcium carbonate.According to another embodiment of the present invention, the calciumcarbonate-comprising material comprises a mixture of two or more groundcalcium carbonates selected from different sources.

“Precipitated calcium carbonate” (PCC) in the meaning of the presentinvention is a synthesized material, generally obtained by precipitationfollowing reaction of carbon dioxide and lime in an aqueous environmentor by precipitation of a calcium and carbonate ion source in water or byprecipitation by combining calcium and carbonate ions, for example CaCl₂and Na₂CO₃, out of solution. Further possible ways of producing PCC arethe lime soda process, or the Solvay process in which PCC is aby-product of ammonia production. Precipitated calcium carbonate existsin three primary crystalline forms: calcite, aragonite and vaterite, andthere are many different polymorphs (crystal habits) for each of thesecrystalline forms. Calcite has a trigonal structure with typical crystalhabits such as scalenohedral (S-PCC), rhombohedral (R-PCC), hexagonalprismatic, pinacoidal, colloidal (C-PCC), cubic, and prismatic (P-PCC).Aragonite is an orthorhombic structure with typical crystal habits oftwinned hexagonal prismatic crystals, as well as a diverse assortment ofthin elongated prismatic, curved bladed, steep pyramidal, chisel shapedcrystals, branching tree, and coral or worm-like form. Vaterite belongsto the hexagonal crystal system. The obtained PCC slurry can bemechanically dewatered and dried.

According to one embodiment of the present invention, the calciumcarbonate-comprising material comprises one precipitated calciumcarbonate. According to another embodiment of the present invention, thecalcium carbonate-comprising material comprises a mixture of two or moreprecipitated calcium carbonates selected from different crystallineforms and different polymorphs of precipitated calcium carbonate. Forexample, the at least one precipitated calcium carbonate may compriseone PCC selected from S-PCC and one PCC selected from R-PCC.

According to one embodiment of the present invention, the calciumcarbonate-comprising material is a ground calcium carbonate. Accordingto another embodiment of the present invention, the calciumcarbonate-comprising material is precipitated calcium carbonate.According to still another embodiment of the present invention, thecalcium carbonate-comprising material is a mixture of ground calciumcarbonate and precipitated calcium carbonate.

A modified calcium carbonate (MCC) may feature a GCC or PCC with asurface and/or internal structure modification. A surface-reactedcalcium carbonate may be prepared, for example, by providing a GCC orPCC in form of an aqueous suspension, and adding an acid to saidsuspension. Suitable acids are, for example, sulphuric acid,hydrochloric acid, phosphoric acid, citric acid, oxalic acid, or amixture thereof. In a next step, the calcium carbonate is treated withgaseous carbon dioxide. If a strong acid such as sulphuric acid orhydrochloric acid is used for the acid treatment step, the carbondioxide will form automatically in situ. Alternatively or additionally,the carbon dioxide can be supplied from an external source.Surface-reacted calcium carbonates are described, for example, in US2012/0031576 A1, WO 2009/074492 A1, EP 2 264 109 A1, EP 2 070 991 A1, orEP 2 264 108 A1. According to one embodiment, the modified calciumcarbonate is a surface-reacted calcium carbonate, preferably obtainedfrom the reaction with sulphuric acid, hydrochloric acid, phosphoricacid, citric acid, oxalic acid, or a mixture thereof, and carbondioxide.

According to one embodiment, the mixed carbonate based fillers areselected from calcium associated with magnesium and analogues orderivatives, various matter such as clay or talc or analogues orderivatives, and mixtures of these fillers, such as, for example,talc-calcium carbonate or calcium carbonate-kaolin mixtures, or mixturesof natural calcium carbonate with aluminium hydroxide, mica or withsynthetic or natural fibres or co-structures of minerals such astalc-calcium carbonate or talc-titanium dioxide or calciumcarbonate-titanium dioxide co-structures.

Examples of aluminium trihydrate are gibbsite or bayerite, and examplesof magnesium hydroxide are brucite or hydromagnesite. Examples ofplastic pigments include styrene pigments and Ropaque™ (The Dow ChemicalCompany, USA).

According to one embodiment of the present invention, the at least onefiller material is provided in form of particles having a volumedetermined median particle diameter d₅₀ of less than or equal to 100 μm,preferably from 0.1 to 100 μm, more preferably from 0.2 to 50 μm, evenmore preferably from 0.5 to 25 μm, and most preferably from 1.0 to 10μm. According to another embodiment of the present invention, the atleast one filler material is provided in form of particles having avolume determined median particle size d₅₀ of 0.3 to 15 μm, preferablyfrom 0.5 to 10 μm, and more preferably from 1.0 to 5.0 μm.

According to a preferred embodiment of the present invention, the atleast one filler material is provided in form of particles having aspecific surface area from 0.1 to 200 m²/g, preferably from 0.5 to 100m²/g, more preferably from 1.0 to 50 m²/g, and most preferably from 2.0to 10 m²/g, measured using nitrogen and the BET method according to ISO9277:2010.

It is a requirement of the present invention that the at least onefiller material is different in the first aqueous suspension S1 and thesecond aqueous suspension S2. Thus, the first aqueous suspension S1comprises at least one first filler material and the second aqueoussuspension S2 comprises at least one second filler material. Optionally,further following suspension can be present (S3 to SN), which maycomprise the same filler material as the first aqueous suspension S1 orthe second aqueous suspension S2 or may comprise at least one differentfiller material.

The at least one filler material in the first aqueous suspension S1 andthe at least one filler material in the second aqueous suspension S2 maydiffer in the type of filler material and/or the volume determinedmedian particle diameter d₅₀ the filler material particles and/or thespecific surface area of the filler material particles and/or crystalmorphology of the filler material and/or the charge of the fillermaterial.

Furthermore, the first aqueous suspension S1 and the second aqueoussuspension S2 may differ in their pH value. For example, the firstaqueous suspension S1 may have a pH value of above 7 and the secondaqueous suspension S2 may have a pH value of below 7, or vice versa. Itis known to the skilled person that the pH value of the suspensions canbe adjusted by the addition of Brønstedt acids or basis. Examples ofsuitable acids are hydrochloric acid, sulphuric acid, phosphoric acid,or citric acid. Examples of suitable basis are sodium hydroxide,potassium hydroxide, or sodium carbonate.

According to one embodiment of the present invention, the at least onefiller material in the first suspension S1 is ground calcium carbonateand the at least one filler material in the second suspension S2 isselected from precipitated calcium carbonate and/or clay. According toanother embodiment of the present invention, the at least one fillermaterial in the first suspension S1 is precipitated calcium carbonatehaving an aragonitic crystal morphology and the at least one fillermaterial in the second suspension S2 is precipitated calcium carbonatehaving a scalenohedral crystal morphology.

According to one embodiment of the present invention, the at least onefiller material in the first suspension S1 has a volume determinedmedian particle diameter d₅₀ of less than or equal to 100 μm, preferablyfrom 0.1 μm to 100 μm, more preferably from 0.2 to 50 μm, and the fillermaterial in the second suspension S2 has a volume determined medianparticle diameter d₅₀ of less than or equal to 100 μm, preferably from0.1 μm to 100 μm, more preferably from 0.2 to 50 μm. According toanother embodiment of the present invention, the at least one fillermaterial in the first suspension S1 has a specific surface area from 0.1to 200 m²/g, preferably from 0.5 μm to 100 m²/g, more preferably from 1μm to 50 m²/g, and most preferably from 1 to 10 m²/g, and the fillermaterial in the second suspension S2 has a specific surface area from0.1 to 200 m²/g, preferably from 0.5 μm to 100 m²/g, more preferablyfrom 1 μm to 50 m²/g, and most preferably from 1 to 10 m²/g, measuredusing nitrogen and the BET method according to ISO 9277:2010.

Flocculating Additive A

According to step i) of the process according to the present invention,a first aqueous suspension S1 comprises at least one flocculatingadditive A.

The at least one flocculating additive A may be selected from anyflocculating additive known in the art, which promotes flocculation bycausing suspended filler particles to form aggregates called flocs, incombination with another additive, preferably another flocculatingadditive, and/or with the filler material alone. The at least oneflocculating additive A may be selected from anionic, non-ionic,zwitter-ionic, amphoteric, or cationic polymers, or mixtures thereof.Preferably, the at least one flocculating additive A is a cationicpolymer.

According to one embodiment of the present invention, the at least oneflocculating additive A is a cationic polymer selected from the groupconsisting of cationic starch, polyamines, polyethyleneimines,polyacrylamides, cationic amine amide, epichlorohydrin resins,polydiallyldimethylammonium chloride, cationic guar and/or mixturesthereof.

According to one embodiment of the present invention, the cationicpolymer is a cationic starch.

The cationic starch is preferably chemically modified with cationicgroups selected from the group comprising amino groups, immonium groups,ammonium groups, sulphonium groups, phosphonium groups, and mixturesthereof. The cationic starch can be chosen from amongst the chemicallymodified starches originating from virtual any natural sources providingfor starch in reasonable amounts. For example, the cationic starch canbe chosen from amongst the chemically modified starches originating fromstarches selected from the group comprising wheat starch, corn starch,rice starch, potato starch, tapioca starch, maranta starch, sorghumstarch and mixtures thereof. In one preferred embodiment, the cationicstarch is selected from those enriched in amylopectin, that is to saythe chemically modified starch is preferably selected from the groupconsisting of rice starch, potato starch, and mixtures thereof. Thecationic starch can also be obtained from genetically modified sourcescomprising amylopectin enriched starches. Methods for preparing suchcationic starches are known by the skilled person. The molecular weightof the cationic starch can range from 1 000 to 1 000 000 g/mol and isgenerally about 220 000 g/mol. The molecular weight of the cationicstarch can be adjusted by the treatment with hydrogen peroxide (H₂O₂).According to one embodiment of the present invention, the cationicpolymer is a polyamine, preferably a polyethyleneimine (PEI) beingselected from the group comprising branched polyethyleneimines, linearpolyethyleneimines and mixtures of the foregoing. Preferably, the ratioof primary, secondary and tertiary amine functions in the branchedpolyethyleneimines is in the range of 1:0.86:0.42 to 1:1.20:0.76, priorto a possible modification of the branched polyethyleneimines.

According to one preferred embodiment of the present invention, thepolyethyleneimine is selected from the group of modified and unmodifiedpolyethyleneimines. Examples for suitable polyethyleneimines arehomopolymers of ethyleneimine (aziridine) or its higher homologues andalso the graft polymers of polyamidoamines or polyvinylamines withethyleneimine or its higher homologues. The polyethyleneimines can becrosslinked or uncrosslinked, quaternized and/or modified by reactionwith alkylene oxides, dialkyl or alkylene carbonates or C₁-C₈-carboxylicacids. The polyethyleneimines may be modified by reaction with alkyleneoxides such as ethylene oxide, propylene oxide or butylene oxide,dialkyl carbonates such as dimethyl carbonate and diethyl carbonate,alkylene carbonates such as ethylene carbonate or propylene carbonate,or C₁-C₈-carboxylic acids. Modified PEIs can include alkoxylatedpolyethyleneimines such as propoxylated polyethyleneimines (PPEIs) andethoxylated polyethyleneimines (EPEIs). Further preferred modifiedpolyethyleneimines can be obtained by reacting the unmodified PEIs withone or more C₁-C₂₈-fatty acids, preferably with one or more C₆-C₁₈-fattyacids and especially preferred with C₁₀-C₁₄-fatty acids, like, forexample, coconut fatty acid.

The polyethyleneimine can have a weight average molecular weight M_(w)in the range of 1 000 g/mol and 1 000 000 g/mol. In another preferredembodiment of the present invention the polyethyleneimine is selectedfrom the group of linear polyethyleneimines having a weight averagemolecular weight M_(w) from 100 to 700 g/mol, and preferably from 146 to232 g/mol, and preferably is selected from triethylenetetramine,pentaethylenehexamine and tetraethylenepentamine. According to anotherpreferred embodiment the polyethyleneimine is selected from the group ofbranched polyethyleneimines having a weight average molecular weightM_(w) from 500 to 8 000 g/mol and preferably from 800 to 1 200 g/mol.

Further examples of cationic polymers that are suitable for the processof the present invention are polyacrylamides, or cationicepichlorohydrin resins.

According to an exemplary embodiment, the polyacrylamides includemonomers of dialkylaminoethyl(meth)acrylates,dialkylaminoethyl(meth)acrylamides, dialkylaminomethyl(meth)acrylamides,and dialkylamino-1,3-propyl(meth)acrylamides, preferably copolymerizedwith nonionic monomers, preferably arylamide.

According to another embodiment, the cationic epichlorohydrin resins arecopolymers comprising as the monomer one or more dicarboxylic acids andone or more monomers from the group of diamines, triamines,dialkanolamines or trialkanolamines and epichlorohydrin.

Preferably saturated or unsaturated, branched or unbranched C₂-C₁₀dicarboxylic acids, preferably C₃-C₉ dicarboxylic acids, C₄-C₈dicarboxylic acids, C₅-C₇ dicarboxylic acids, in particular adipic acidare used as the dicarboxylic acid monomers. Especially suitable as thesecond monomer of the flocculating additive A are linear and branched,substituted and unsubstituted diamines and triamines, in particularN-(2-aminoethyl)-1,2-ethanediamine. Preferably used dialkanolamines andtrialkanolamines include, for example, diethanolamine,N-alkyl-dialkanolamines such as N-methyl and N-ethyldiethanolamine andtriethanolamine. For monitoring and control of the molecular weightand/or the chain length, one or more monovalent amines such asmonoalkanolamines may be used during the polycondensation. Monoethanolis used preferably. The resulting intermediate product is reactedfurther with epichlorohydrin.

According to a preferred embodiment of the present invention, thecationic epichlorohydrin resin is a copolymer of adipic acid withN-(2-aminoethyl)-1,2-ethanediamine and epichlorohydrin.

According to still another embodiment of the present invention, thecationic polymer is polydiallyldimethylammonium chloride (polyDADMAC).

PolyDADMAC (polydiallyldimethylammonium chloride) is a linearhomopolymer of diallyldimethylammonium chloride (DADMAC) having thefollowing structure:

The linear homopolymer formed from a monomer that has a quaternaryammonium and two unsaturated —CH═CH₂ functionalities is polymerized byfree-radical polymerization of the DADMAC. In the polyDADMAC structurequaternary ammonium groups are on rings that are included in thebackbone of the polymer chain. This composition means that thepolyDADMAC macromolecules tend to be quite stiff, having a longerpersistence length than, for instance, polyamines. For this reason,polyDADMAC is expected to have a more extended conformation in solution.The polyDADMAC can have a weight average molecular weight M_(w) in therange from 10 000 to 1 000 000 g/mol and preferably in the range from100 000 to 500 000 g/mol.

According to still another embodiment of the present invention, thecationic polymer is a cationic guar.

Guar comprises a natural heteropolysaccharide (guaran) consisting ofgalactose units and mannose units usually in the ratio of 1:2 and is theendosperm component of guar seeds. In general, guar comprises a linearchain of 1,4-linked β-D-mannopyranosyl units with 1,6-linkedα-D-galactopyranosyl units. Guar seeds containing about 14 to 17 wt.-%husk, 35 to 42 wt.-% endosperm and 43 to 47 wt.-% embryo, are usuallydry-milled and screened to separate out the endosperm which is theindustrial guar of commerce. A guar derivative can be obtained, forexample, by modifying the heteropolysaccharide through the use ofenzymes, acids, oxidation media, temperature, radiation etc. Methods forpreparing such guar derivatives are known to the skilled person. Forexample, a modification may be obtained by the use of a commerciallyavailable α-D-galactosidase enzyme which is useful to removeα-D-galactopyranosyl units. By controlling the length of time that theguaran is exposed to the α-D-galactosidase enzyme, the extent of removalof α-D-galactopyranosyl units from the linear chain of mannose units canbe controlled. A cationic guar can be obtained by reacting guar withderivatives of quaternary ammonium salts.

The at least one flocculating additive A may comprise one or more of theaforementioned cationic polymers and one or more further flocculatingadditives known in the art. According to one embodiment of the presentinvention, the at least one flocculating additive A is a mixture of twoor more of the aforementioned cationic polymers. According to anotherembodiment of the present invention, the at least one flocculatingadditive A consists of one of the aforementioned cationic polymers.According to one preferred embodiment, the at least one flocculatingadditive A is cationic starch.

The at least one flocculating additive A can be provided in an aqueousform, e.g., in the form of a water-based solution, or in form of anorganic solution, e.g., in an organic solvent selected from the groupcomprising methanol, ethanol, acetone, and mixtures thereof. However,the at least one flocculating additive A also may be provided in form ofan emulsion or a dispersion of water and/or organic solvents, or in formof a mixture of a solution and/or an emulsion and/or a dispersion ofwater and/or organic solvents.

If the at least one flocculating additive A is provided in form of asolution, the solution is preferably prepared in that the at least oneflocculating additive A is added to a solvent, preferably water, havinga temperature of at least 50° C., preferably from 50° C. to 100° C.,more preferably from 60° C. to 98° C. and most preferably from 70° C. to96° C. For example, the solution is prepared in that the at least onecationic polymer is added to water having a temperature of from 80° C.to 96° C., like from 90° C. to 96° C. Alternatively, the solution isprepared in that the at least one flocculating additive A is added to asolvent, preferably water, having a temperature of below 50° C.,preferably from 5° C. to 49° C., more preferably from 10° C. to 40° C.and most preferably from 15° C. to 30° C.

In one preferred embodiment, a solution of the at least one flocculatingadditive A is prepared in that the at least one flocculating additive Ais added to water at about room temperature, i.e. at 20° C.±2° C.

According to an alternative embodiment, the at least one flocculatingadditive A is provided in dry form, e.g. in form of a dry powder.

In case the at least one flocculating additive A is provided in the formof a dispersion, the particle size of the flocculating additive A canhave a d₅₀ value from 10 to 500 nm, preferably from 20 to 100 nm, andmore preferably from 25 to 80 nm.

The flocculating additive A may be provided in form of a solution or drymaterial, preferably in form of a solution having a concentration from0.5 to 70 wt.-%, preferably from 1 to 25 wt.-%, more preferably from 1.5to 20 wt.-%, and most preferably from 2 to 10 wt.-%, based on the totalweight of the solution.

According to one embodiment of the present invention, the content of theat least one flocculating additive A in the first aqueous suspension S1is from 0.001 to 20 wt.-%, more preferably from 0.5 to 10 wt.-%, andmost preferably from 3 to 5 wt.-%, based on the total weight of thefirst aqueous suspension S1. According to another embodiment of thepresent invention, the content of the at least one flocculating additiveA in the first aqueous suspension S1 is from 0.001 to 20 wt.-%, morepreferably from 0.5 to 10 wt.-%, and most preferably from 3 to 5 wt.-%,based on the total dry weight of the at least one filler material in thefirst aqueous suspension S1. According to still another embodiment ofthe present invention, the content of the at least one flocculatingadditive A in the first aqueous suspension S1 is from 0.001 to 20 wt.-%,more preferably from 0.5 to 10 wt.-%, and most preferably from 3 to 5wt.-%, based on the total dry weight of the at least one filler materialin the aqueous suspension SM.

Flocculating Agent B

According to step ii) of the process according to the present invention,a second aqueous suspension S2 comprises at least one flocculatingadditive B which is different from flocculating additive A.

The at least one flocculating additive B may be selected from anyflocculating additive known in the art, which is different fromflocculating additive A and promotes flocculation by causing suspendedfiller particles to form aggregates called flocs, in combination withanother additive, preferably another flocculating additive, and/or withthe filler material alone. The at least one flocculating additive B maybe selected from anionic, non-ionic, zwitter-ionic, amphoteric, orcationic polymers, or mixtures thereof. According to one embodiment, theat least one flocculating additive A and the at least one flocculatingadditive B are oppositely charged.

According to a preferred embodiment of the present invention, the atleast one flocculating additive B is an anionic polymer, and morepreferably a modified polysaccharide.

“Modified polysaccharides” in the meaning of the present invention arepolysaccharides, wherein at least a part of the hydroxyl groups iscarboxylated. Additionally, the modified polysaccharides may containother modifications such as aldehyde groups.

Modified polysaccharides according to the present invention may comprisethe following structure:

wherein a part of the hydroxyl groups is carboxylated and “n” isindirectly represented by the intrinsic viscosity.

Polysaccharides are polymeric carbohydrate structures, formed ofrepeating units (at least 10) joined together by glycosidic bonds.Depending on the spatial arrangement of the glycosidic bonds, one maydistinguish between α- and β-glycosidic bonds. These structures may belinear, but may also contain various degrees of branching.Polysaccharides may also contain slight modifications of the repeatingunit. Exemplary polysaccharides are starch, cellulose, or glycogen, butalso structural polysaccharides such as cellulose and chitin.

According to one embodiment of the present invention, the at least onemodified polysaccharide has a degree of substitution of thehydroxyl-groups in the range from 0.4 to 2.0, preferably from 0.5 to1.8, more preferably from 0.6 to 1.6, and most preferably from 0.7 to1.5.

According to one embodiment of the present invention, the modifiedpolysaccharide is a carboxymethyl derivate and/or a carboxymethylhydroxypropyl derivate and/or a carboxymethyl hydroxyethyl derivate of apolysaccharide. For example, the modified polysaccharide can be acarboxymethylcellulose (CMC), an anionic starch, an anionic guar,anionic xanthan gum, or mixtures thereof.

According to one embodiment of the present invention, the at least oneflocculating additive B is an anionic polymer selected from the groupconsisting of carboxymethyl cellulose, anionic starch, anionic guar,anionic xanthan gum and/or mixtures thereof.

According to one embodiment of the present invention, the at least oneflocculating additive B is carboxymethylcellulose (CMC).

Carboxymethylcellulose (CMC) may be prepared from cellulose by reactionwith monochloroacetic acid in the presence of caustic soda to form thesodium salt of carboxymethylcellulose. Each repeating D-glycose unitcontains three hydroxyl groups capable of etherification, to give amaximum charge density of three carboxylic groups per monomer unit (i.e.a degree of substitution of three).

The molecular weight and the intrinsic viscosity of thecarboxymethylcellulose-based polymer can be adjusted by any method thatis known to the person skilled in the art, e.g., by addition ofperoxides. Reference is made to DE 1 543 116 A1 describing a method forthe preparation of low viscous, water-soluble CMC by oxidativedegradation with H₂O₂ and to DE 44 11 681 A1 describing the dependencyof the degradation of polysaccharide ether on the amount of oxidizingagent, temperature and duration of the treatment.

According to a preferred embodiment of the present invention, thecarboxymethylcellulose has an intrinsic viscosity in the range from 5 to500 ml/g, preferably from 10 to 450 ml/g, more preferably from 50 to 350ml/g and most preferably from 100 to 200 ml/g.

According to another embodiment of the present invention, the at leastone flocculating additive B is an anionic starch.

The anionic starch is preferably chemically modified with anionic groupsselected from the group comprising carboxyl groups, carboxymethylgroups, carboxymethyl hydroxypropyl groups, carboxymethyl hydroxyethylgroups, phosphate groups, sulphonate groups and mixtures thereof. Theanionic starch can be chosen from amongst the chemically modifiedstarches originating from starches selected from the group comprisingwheat starch, corn starch, rice starch, potato starch, tapioca starch,maranta starch, sorghum starch and mixtures thereof. The anionic starchcan also be obtained from genetically modified sources comprisingamylopectin enriched starches. In one preferred embodiment, the anionicstarch is selected from those enriched in amylopectin, that is to saythe chemically modified starch is preferably selected from the groupconsisting of rice starch, potato starch, and mixtures thereof. Methodsfor preparing such anionic starches are known by the skilled person. Themolecular weight of the anionic starch can range from 1 000 to 1 000 000g/mol and is generally about 220 000 g/mol. The molecular weight of theanionic starch can be adjusted by the treatment with hydrogen peroxide(H₂O₂).

According to still another preferred embodiment of the presentinvention, the at least one flocculating additive B is an anionic guar.

Guar comprises a natural heteropolysaccharide (guaran) consisting ofgalactose units and mannose units usually in the ratio of 1:2 and is theendosperm component of guar seeds. In general, guar comprises a linearchain of 1,4-linked β-D-mannopyranosyl units with 1,6-linkedα-D-galactopyranosyl units. Guar seeds containing about 14 to 17 wt.-%husk, 35 to 42 wt.-% endosperm and 43 to 47 wt.-% embryo, are usuallydry-milled and screened to separate out the endosperm which is theindustrial guar of commerce. A guar derivative can be obtained, forexample, by modifying the heteropolysaccharide through the use ofenzymes, acids, oxidation media, temperature, radiation etc. Methods forpreparing such guar derivatives are known to the skilled person. Forexample, a modification may be obtained by the use of a commerciallyavailable α-D-galactosidase enzyme which is useful to removeα-D-galactopyranosyl units. By controlling the length of time that theguaran is exposed to the α-D-galactosidase enzyme, the extent of removalof α-D-galactopyranosyl units from the linear chain of mannose units canbe controlled. Additionally or alternatively, a modification of guar maybe obtained by etherification of guar with propyleneoxide orethyleneoxide resulting in a hydroxypropyl guar or hydroxyethyl guar.

According to one embodiment of the present invention, the anionic guaris a carboxymethyl guar (CMG) and/or a carboxymethyl hydroxypropyl guar(CMHPG) and/or a carboxymethyl hydroxyethyl guar (CMHEG). For example,carboxymethyl guar is obtained by reacting a guar with monochloroaceticacid in the presence of caustic soda.

Xanthan gum is a polysaccharide secreted by the bacterium Xanthomonascampestris and is typically composed of pentasaccharide repeat units,comprising glucose, mannose, and glucuronic acid. It can be produced bythe fermentation of glucose, sucrose, or lactose.

The at least one flocculating additive B may comprise one or more of theaforementioned anionic polymers and one or more further flocculatingadditives known in the art. According to one embodiment of the presentinvention, the at least one flocculating additive B is a mixture of twoor more of the aforementioned anionic polymers. According to anotherembodiment of the present invention, the at least one flocculatingadditive B consists of one of the aforementioned anionic polymers.According to one preferred embodiment, the at least one flocculatingadditive B is anionic carboxymethyl cellulose.

According to one embodiment of the present invention, the at least oneflocculating additive B employed in the process according to the presentinvention has a pH from 4.5 to 12, preferably from 7 to 11, and morepreferably from 8.0 to 10.5.

The at least one flocculating additive B can be provided as solution ordry material. According to a preferred embodiment, the at least oneflocculating additive B is in form of an aqueous solution.

According to a preferred embodiment of the present invention, the atleast one flocculating additive B is in form of an aqueous solutionhaving a concentration from 1 to 70 wt.-%, preferably from 2 to 55wt.-%, more preferably from 5 to 50 wt.-%, and most preferably from 30to 50 wt.-%, based on the total weight of the solution.

If desired, the solution of the at least one flocculating additive B canbe concentrated, for example, by ultrafiltration or thermal or drying.Dry flocculating additive B can be produced by thermal drying,preferably by spray drying, and may have a solids content of more than90 wt.-%, preferably from 95 to 99.9 wt.-%, based on the total weight ofthe flocculating additive B.

According to one embodiment of the present invention, the content of theat least one flocculating additive B in the second aqueous suspension S2is from 0.001 to 20 wt.-%, more preferably from 0.1 to 10 wt.-%, andmost preferably from 0.2 to 0.8 wt.-%, based on the total weight of thesecond aqueous suspension S2. According to another embodiment of thepresent invention, the content of the at least one flocculating additiveB in the second aqueous suspension S2 is from 0.001 to 20 wt.-%, morepreferably from 0.1 to 10 wt.-%, and most preferably from 0.2 to 0.8wt.-%, based on the total dry weight of the at least one filler materialin the second aqueous suspension S2. According to still anotherembodiment of the present invention, the content of the at least oneflocculating additive B in the second aqueous suspension S2 is from0.001 to 20 wt.-%, more preferably from 0.1 to 10 wt.-%, and mostpreferably from 0.2 to 0.8 wt.-%, based on the total dry weight of theat least one filler material in the aqueous suspension SM.

Process for Preparation of Flocculated Filler Particles

According to the present invention a process for the preparation offlocculated filler particles is provided, comprising the steps of

-   -   a) providing at least two aqueous suspensions each comprising at        least one filler material, characterized in that        -   i) a first aqueous suspension S1 comprises at least one            flocculating additive A, and        -   ii) a second aqueous suspension S2 comprises at least one            flocculating additive B which is different from flocculating            additive A, and        -   iii) the at least one filler material in the first aqueous            suspension S1 and the second aqueous suspension S2 is            different, and    -   b) combining the at least two aqueous suspensions provided in        step a) by bringing them together to form an aqueous suspension        SM of flocculated filler particles, wherein the mass ratio of        the at least one filler material in the first aqueous suspension        and the second aqueous suspension S1:S2 is from 1:100 to 100:1.

According to the present invention, the at least one filler material inthe first aqueous suspension S1 and the at least one filler material inthe second aqueous suspension S2 are different. Thus, a first aqueoussuspension S1 is provided comprising at least one flocculating additiveA and at least one first filler material, and a second aqueoussuspension S2 is provided comprising at least one flocculating additiveB which is different from flocculating additive A, and at least onesecond filler material.

According to one embodiment, a first aqueous suspension S1 comprising atleast one flocculating additive A is prepared by

-   -   A1) providing a first aqueous suspension of the at least one        filler material, and    -   A2) adding the at least one flocculating additive A to the first        aqueous suspension of step A1).

According to another embodiment, a first aqueous suspension S1comprising at least one flocculating additive A is prepared by

-   -   A1′) mixing the at least one flocculating additive A with water,        and    -   A2′) adding the at least one filler material to the first        aqueous suspension of step A1′).

According to still another embodiment, a first aqueous suspension S1comprising at least one flocculating additive A is prepared by mixingthe at least one filler material, the at least one flocculating additiveA and water simultaneously.

According to one embodiment, a second aqueous suspension S2 comprisingat least one flocculating additive B is prepared by

-   -   B1) providing a second aqueous suspension of the at least one        filler material, and    -   B2) adding the at least one flocculating additive B to the        second aqueous suspension of step B1).

According to another embodiment, a second aqueous suspension S2comprising at least one flocculating additive B is prepared by

-   -   B1′) mixing the at least one flocculating additive B with water,        and    -   B2′) adding the at least one filler material to the second        aqueous suspension of step B1′).

According to still another embodiment, a second aqueous suspension S2comprising at least one flocculating additive B is prepared by mixingthe at least one filler material, the at least one flocculating additiveB and water simultaneously.

The first aqueous suspension S1 of step i) and/or the second aqueoussuspension S2 of step ii) may be mixed in order to distribute theflocculating additive throughout the aqueous suspension morehomogeneously. Suitable process equipment for mixing is known to theskilled person and also described below.

The at least one filler material, the at least one flocculating additiveA, and the at least one flocculating additive B may be provided in anyof the forms described above. In other words, the at least one fillermaterial may be provided in form of a suspension, slurry, dispersion,paste, powder, a moist filter cake or in pressed or granulated form, andthe flocculating additives may be provided in form of a solution or indry form.

The skilled person will provide the at least one flocculating additive Aand the at least one flocculating additive B in an amount, which leadsto a flocculation of the filler material particles when the firstaqueous suspension S1 and the second aqueous suspension S2 are combined.It is appreciated that flocculation of the filler material particles canalready take place in the first aqueous suspension S1 and/or the secondaqueous suspension S2, before these suspensions are combined. In casethat the flocculation occurs with the filler material alone, thisflocculation can be distinguished from the flocculation, which occursafter combining step b) of the process of the present invention. Forexample, the flocs which form after the process step b) may have adifferent particle size than the flocs generated from one flocculatingagent and the mineral filler alone. The flocs which form after theprocess step b) may be bigger than the flocs generated from oneflocculating agent and the mineral filler alone, or, in case, processstep b) is carried out under shear, the generated flocs may be smallerthan the flocs generated from one flocculating agent and the mineralfiller alone.

According to one embodiment of the present invention, the at least oneflocculating additive B is provided in an amount such that the contentof the at least one flocculating additive A in the first aqueoussuspension S1 is from 0.001 to 20 wt.-%, more preferably from 0.5 to 10wt.-%, and most preferably from 3 to 5 wt.-%, based on the total weightof the first aqueous suspension S1, and/or the at least one flocculatingadditive B is provided in an amount such that the content of the atleast one flocculating additive B in the second aqueous suspension S2 isfrom 0.001 to 20 wt.-%, more preferably from 0.1 to 10 wt.-%, and mostpreferably from 0.2 to 0.8 wt.-%, based on the total weight of thesecond aqueous suspension S2.

According to one embodiment of the present invention, the mass ratio ofthe at least one flocculating additive A and the at least oneflocculating additive B is from 1:50 to 50:1, preferably from 1:30 to30:1, more preferably from 1:20 to 20:1, even more preferably from 1:10to 10:1, and most preferably from 1:8 to 8:1. The mass ratios are basedon the dry weight of the at least flocculating additive A and the atleast one flocculating additive B.

According to step b) of the process according to the present invention,the at least two suspensions provided in step a) are combined bybringing them together, preferably they are combined by bringing themtogether simultaneously. However, it is within the scope of presentinvention to combine the aqueous suspension in any order.

The at least two suspensions may be combined by any means known in theart, for example, by pouring, injecting or discharging. For example, theat least two suspensions provided in step a) may be combined by pouring,injecting or discharging them together into another reservoir, vessel orpipe. According to another example, the at least two suspensionsprovided in step a) may be combined by pouring, injecting or dischargingone of the at least two suspensions into the remaining and/or furthersuspension(s).

The process step b) may be carried out at room temperature, i.e. at 20°C.±2° C., or at other temperatures. According to one embodiment processstep b) is carried out at a temperature from 5 to 100° C., preferablyfrom 10 to 80° C., and most preferably from 20 to 65° C. Heat may beintroduced by internal shear or by an external source or a combinationthereof.

According to one embodiment of the present invention, process step b) iscarried out for at least 1 s, preferably for at least 1 min, e.g., forat least 15 min, 30 min, 1 hour, 2 hours, 4 hours, 6 hours, 8 hours, or16 hours.

According to one embodiment of the present invention, the aqueoussuspension SM is sheared during and/or after process step b). “Shearing”in the meaning of the present invention refers to inducing a shearstress within a material, for example, the aqueous suspension SM. Byshearing the floc size of the flocculated filler particles may bereduced and a more homogeneous distribution of the particle size of theflocculated filler particles may be obtained. FIG. 3 illustrates ashearing process, wherein larger flocculated filler particles (greycircles) are desaggregated under shear induced by a static mixer intosmaller flocs.

The aqueous suspensions SM may be sheared by any method known theskilled person. Examples of suitable shearing methods are shaking,mixing, stirring, agitating, milling, ultrasonication, or inducing aturbulent or laminar flow by means such as baffles or lamellas.

Suitable shearing equipment is known to the skilled person, and may beselected, for example, from stirrers, such as rotor stator systems,blade stirrers, propeller stirrers, turbine stirrers, or anchorstirrers, static mixers such as pipes including baffles or lamellas,mills such as ball mills or impact crushers. According to a preferredembodiment of the present invention, a rotor stator stirrer system isused.

According to one embodiment of the present invention, the aqueoussuspension SM is sheared during and/or after process step b) by mixingthe aqueous suspension SM of flocculated filler particles. The mixingmay be done, e.g. by high speed stirring or agitation. Such agitation orstirring can be carried out continuously or discontinuously. The skilledperson will adapt the mixing conditions such as the mixing speed andtemperature according to his process equipment. For example, the mixingmay take place by means of a ploughshare mixer. Ploughshare mixersfunction by the principle of a fluidized bed produced mechanically.Ploughshare blades rotate close to the inside wall of a horizontalcylindrical drum and convey the components of the mixture out of theproduct bed and into the open mixing space. The fluidized bed producedmechanically ensures intense mixing of even large batches in a veryshort time.

Choppers and/or dispersers are used to disperse lumps in a dryoperation. Equipment that may be used in the inventive process isavailable, for example, from Gebrüder Lödige Maschinenbau GmbH, Germanyor from Silverson (U.S.A.). Furthermore, a tubular mixing apparatus, forexample, from Ystral GmbH, Ballrechten-Dottingen, Germany may be used.Another equipment type that may be used in the inventive process is aMEGATRON® inline homogenizer from Kinematika AG, Switzerland.

According to one embodiment the process is carried out under shear in atleast two steps at different shear rates, preferably the first shearrate is lower than the second shear rate. Preferably the first shearingstep is carried out during step b) with a shearing rate <1 000 s⁻¹. Thesecond shearing step is preferably carried out after process step b).The second shear rate can be from 1 000 to 1 000 000 s⁻¹, preferablyfrom 3 000 to 600 000 s⁻¹, more preferably from 6 000 to 300 000 s⁻¹,and most preferably from 10 000 to 100 000 s⁻¹.

According to one embodiment of the present invention, the aqueoussuspension SM is sheared during process step b). According to anotherembodiment of the present invention, the aqueous suspension SM issheared after process step b). According to still another embodiment ofthe present invention, the aqueous suspension SM is sheared during andafter process step b).

According to a further embodiment of the present invention, the firstaqueous suspension S1 and/or the second aqueous suspension S2 providedin step a) of the inventive process are sheared before process step b).The aqueous suspensions may be sheared by any method known the skilledperson, and in particular by the methods described above.

According to a further embodiment of the present invention, furtheraqueous suspensions comprising at least one filler material are providedin process step a). The further aqueous suspensions may comprise thesame filler material as the first aqueous suspension S1 or the secondaqueous suspension S2 or may comprise at least one different fillermaterial. Optionally, the further aqueous suspensions may comprise atleast one flocculating additive, which may be selected from the at leastone flocculating additive A and/or the at least one flocculatingadditive B described above. For example, a third aqueous suspension S3comprising at least one filler material may be provided in process stepa), which comprises the same material as the first aqueous suspension S1or the second aqueous suspension S2 or may comprise a different fillermaterial. Furthermore, the third aqueous suspension S3 may comprise atleast one flocculating additive which may be selected from the at leastone flocculating additive A and/or the at least one flocculatingadditive B described above.

According to one embodiment of the present invention, the Brookfieldviscosity of the first aqueous suspension S1 and/or the second aqueoussuspension S2 and/or the aqueous suspension SM is less than 5 000 mPa·sat 25° C., preferably less than 1 000 mPa·s at 25° C., and morepreferably between 10 and 200 mPa·s at 25° C.

According to a preferred embodiment, the Brookfield viscosity of thefirst aqueous suspension S1, the second aqueous suspension S2, and theaqueous suspension SM is less than 5 000 mPa·s at 25° C., preferablyless than 1 000 mPa·s at 25° C., and more preferably between 10 and 200mPa·s at 25° C. According to one embodiment, the aqueous suspension SMof flocculated filler materials has a Brookfield viscosity from 1 to1000 mPa·s at 25° C., more preferably from 5 and 800 mPa·s at 25° C.,and most preferably from 10 and 600 mPa·s at 25° C. According to oneembodiment, the Brookfield viscosity is measured at 100 rpm. Theviscosity of the first aqueous suspension S1 and/or the second aqueoussuspension S2 and/or the aqueous suspension SM may be adjusted by theaddition of a solvent, preferably water.

The solids content of the aqueous suspension SM can be adjusted by themethods known to the skilled person. To adjust the solids content of anaqueous suspension, the suspension may be partially or fully dewateredby a filtration, centrifugation or thermal separation process. Forexample, the suspensions may be partially or fully dewatered by afiltration process such as nanofiltration or a thermal separationprocess such as an evaporation process. Alternatively, water may beadded to the solid material (e.g. resulting from filtration) until thedesired solids content is obtained. Additionally or alternatively, aflocculated filler particle suspension or other filler particlesuspension having an appropriate lower content of solid particles may beadded to the aqueous suspension SM until the desired solids content isobtained. The additionally added flocculated filler particle suspensionor other filler particles suspensions can be dispersed or undispersed.

According to one embodiment of the present invention, the solids contentof the aqueous suspension SM obtained after process step b) is from 1 to75 wt.-%, preferably from 2 to 60 wt.-%, and most preferably from 5 to35 wt.-%, based on the total weight of the aqueous suspension SM.

Process step b) can be carried out in form of a batch process, asemi-continuous or a continuous process.

As shown in FIG. 1, a batch process may comprise of a first vessel (1),a second vessel (2), and a mixing vessel (3). The first vessel (1) maycontain a first aqueous suspension (4) containing at least one firstfiller material. The second vessel (2) may contain a second aqueoussuspension (5) containing at least one second filler material, which isdifferent to that included in the first vessel (1). At least oneflocculating additive A (6) may be added to the first vessel (1) andmixed with the first aqueous suspension (4) containing at least onefirst filler material. At least one flocculating additive B (7) may beadded to the second vessel (2) and mixed with the second aqueoussuspension (5) containing at least one second filler material. Theobtained mixtures may then be combined by discharging themsimultaneously into the mixing vessel (3).

In a continuous process the desired amount of the first flocculatingadditive A may be injected into a first pipe containing a first aqueoussuspension containing at least one first filler material, and thedesired amount of the second flocculating additive B may be injectedinto a second pipe containing a second aqueous suspension containing atleast one second filler material which is different to that included inthe first pipe. The first and the second pipe may be of a lengthsufficient to permit adequate mixing of the at least one filler materialand the flocculating additives and/or may comprise an in-line staticmixer. The first and the second suspensions may be pumped and injectedsimultaneously to a third pipe, wherein the first and the secondsuspensions are combined.

According to one embodiment of the present invention, the flocculatedfiller particles obtained by process step b) are characterized in thatthey have a volume determined median particle diameter d₅₀ from 0.1 to500 μm, preferably from 0.2 to 200 μm, more preferably from 0.5 to 150μm, and most preferably from 1.0 to 100 μm. According to anotherembodiment of the present invention, the flocculated filler particlesobtained by process step b) are characterized in that they have a volumedetermined median particle diameter d₅₀ from 0.1 to 70 μm, preferablyfrom 0.2 to 50 μm, more preferably from 0.5 to 30 μm, and mostpreferably from 1.0 to 15 μm.

According to the present invention a process for the preparation offlocculated filler particles is provided, comprising the steps of

-   -   a) providing at least two aqueous suspensions each comprising at        least one filler material, characterized in that        -   i) a first aqueous suspension S1 comprises at least one            flocculating additive A, and        -   ii) a second aqueous suspension S2 comprises at least one            flocculating additive B which is different from flocculating            additive A, and        -   iii) the at least one filler material in the first aqueous            suspension S1 and the second aqueous suspension S2 is            different, and    -   b) combining the at least two aqueous suspensions provided in        step a) by bringing them simultaneously together to form an        aqueous suspension SM of flocculated filler particles, wherein        the mass ratio of the at least one filler material in the first        aqueous suspension and the second aqueous suspension S1:S2 is        from 1:100 to 100:1, and        -   wherein the at least one filler material is selected from a            calcium carbonate-comprising material, preferably ground            calcium carbonate and/or precipitated calcium carbonate,            and/or clay,        -   the at least one flocculating additive A is a cationic            starch, and        -   the at least one flocculating additive B is a carboxymethyl            cellulose.

Preferably, the at least one filler material in the first aqueoussuspension S1 is selected from a calcium carbonate-comprising material,preferably ground calcium carbonate, and the at least one fillermaterial in the second aqueous suspension S2 is selected fromprecipitated calcium carbonate and/or clay, the at least oneflocculating additive A is a cationic starch, and the at least oneflocculating additive B is a carboxymethyl cellulose. According to apreferred embodiment, in process step a) two aqueous suspensions eachcomprising at least one filler material are provided. In addition oralternatively, the content of the at least one flocculating additive Ain the first aqueous suspension S1 is preferably from 0.0001 to 20wt.-%, based on the total weight of the first aqueous suspension S1,and/or the content of the at least one flocculating additive B in thesecond aqueous suspension S2 is preferably from 0.0001 to 20 wt.-%,based on the total weight of the second aqueous suspension S2. Inaddition or alternatively, the content of the at least one fillermaterial in the first aqueous suspension S1 is preferably from 10 to 40wt.-%, based on the total weight of the first aqueous suspension S1,and/or the content of the at least one filler material in the secondaqueous suspension S2 is preferably from 10 to 40 wt.-%, based on thetotal weight of the second aqueous suspension S2. In addition oralternatively, the solids content of the aqueous suspension SM obtainedafter process step b) is preferably from 5 to 35 wt.-%, based on thetotal weight of the aqueous suspension SM.

The Flocculated Filler Particles

According to another aspect of the present invention, a flocculatedfiller particle suspension obtained by a process according to thepresent invention is provided, characterized in that the fillerparticles have a mono-modal particle size distribution and/or a volumedefined particle size polydispersity expressed as full width at halfmaximum height (FWHM) of less than 45 μm and/or a volume determinedmedian particle size (d₅₀) in the range from 5 to 50 μm.

According to still another aspect of the present invention, aflocculated filler particle suspension is provided, characterized inthat the filler particles have a mono-modal particle size distributionand/or a volume defined particle size polydispersity expressed as fullwidth at half maximum height (FWHM) of less than 45 μm and/or a volumedetermined median particle size (d₅₀) in the range from 5 to 50 μm.

According to one embodiment the volume determined median particle size(d₅₀) is from 10 to 30 μm, and preferably from 15 to 25 μm.

According to one embodiment of the present invention, the flocculatedfiller particles have a volume defined particle size polydispersityexpressed as full width at half maximum height (FWHM) of less than 35μm, preferably less than 30 μm, more preferably less than 20 μm, andmost preferably less than 10 μm. According to another embodiment of thepresent invention, the flocculated filler particles have a volumedefined particle size polydispersity expressed as full width at halfmaximum height (FWHM) from 0.01 to 35 μm, preferably from 0.1 to 30 μm,more preferably from 1 to 20 μm, and most preferably from 5 to 10 μm. Asalready defined above, in case that the particle size distribution isnot mono-modal, the full width at half maximum height (FWHM) relates tothe main peak of the particle size distribution, i.e. the peak of theparticle size distribution having the largest area under the curve.

The inventors of the present invention surprisingly found that by mixingthe at least one filler material with each flocculating additiveseparately, and combining the filler material/flocculating additivemixtures afterwards, a more homogeneous or unitary mixture of fillermaterial and flocculating additives can be achieved. This in turn canresult in a more homogeneous particle size distribution of theflocculated filler particles, which may be reflected by a narrowmono-modal distribution of the particle size or, in case that theparticle size distribution is not mono-modal, may be reflected by theabsence of particle populations having a smaller volume determinedmedian particle size (d₅₀) than the main peak of the particle sizedistribution, i.e. the peak having the largest area under the curve.

Preferred flocculated filler particle suspensions are obtained by usingS-PCC as first filler material and GCC as second filler material, GCC asfirst filler material and S-PCC as second filler material, clay as firstfiller material and GCC as second filler material, clay as first fillermaterial and S-PCC as second filler material, aragonitic PCC as firstfiller material and S-PCC as second filler material or clay as firstfiller material and GCC as second filler material. It is preferred toadd carboxymethyl cellulose as flocculating additive A to the firstfiller material and starch as flocculating additive B to the secondfiller material. A preferred ratio between carboxymethyl cellulose andstarch is 1:8.

Furthermore, the inventors surprisingly found that paper productsprepared from the flocculated filler particle suspension of the presentinvention exhibit an improved strength, and also allow the production ofpapers with high content of filler material. Another advantage is thatthe physical and optical properties of the papers prepared from theinvention suspension are not impaired to any substantial degree comparedto papers produced by conventional processes.

According to a further aspect of the present invention, a process forthe preparation of a fleece comprising the steps a) and b) of theprocess according to the present invention is provided, characterized inthat the aqueous suspension SM of flocculated filler particles obtainedafter process step b) is combined in a further step c) with syntheticand/or natural fibres, and the resulting suspension SMF is subjected toa dewatering step d) to obtain a fleece. The aqueous suspension SM offlocculated filler particles can be combined with dry synthetic and/ornatural fibres or with an aqueous suspension of these fibres, preferablywith an aqueous suspension and most preferably with an aqueoussuspension of natural fibres. The content of flocculated fillerparticles and synthetic or natural fibres in the aqueous suspensionduring step c) can be between 0.1 and 5 wt.-%, preferably between 0.5and 3 wt.-% and most preferably about 1 wt.-%, based on the total weightof the aqueous suspension. According to one embodiment, the mass ratioof the flocculated filler particles and the synthetic and/or naturalfibres is between 1:4 and 1:1, preferably between 1:2 and 1:1.Preferably, the process step c) is carried out in the head box of apaper machine.

According to one embodiment of the present invention, the fleece ispaper, cardboard, or containerboard, and preferably a sheet of paper.

The synthetic and/or natural fibres may be selected from any fibressuitable for papermaking known in the art. Examples of synthetic fibresare nylon, polyester, or acrylic fibres. Examples of natural fibres arecellulose pulp derived from wood, rags, grasses, or agricultural wastes.

The skilled person may carry out the dewatering step by any means knownin the art. According to one embodiment the dewatering step d) iscarried out on a screen, preferably via a head box of a paper machine.

According to a further aspect of the present invention, a fleece,preferably a sheet of paper, obtained by steps a) to d) of theafore-mentioned process is provided.

According to one embodiment the fleece is a sheet of paper having apaper weight of 30 to 500 g/m², preferably of 50 to 200 g/m², and morepreferably 80 to 150 g/m². According to one exemplary embodiment, thesheet of paper is a copy paper.

The obtained fleece may have a filler content from 0.1 to 80 wt.-%,based on the total weight of the fleece, preferably from 1 to 60 wt.-%,more preferably from 5 to 40 wt.-%, and most preferably from 10 to 30wt.-%.

According to a further aspect of the present invention, a use of aflocculated filler particle suspension according to the presentinvention in paper coating and/or paper wet end applications, preferablyin high filler load paper wet end applications, or for cigarette paperis provided.

The scope and interest of the invention will be better understood basedon the following figures and examples which are intended to illustratecertain embodiments of the invention and are non-limitative.

DESCRIPTION OF THE FIGURES

FIG. 1 shows an example of a batch process of the present invention.

FIG. 2 shows the particle size distribution of filler particlesaccording to example 2 (sample 6).

FIG. 3 illustrates floc desaggregation under shear using a static mixer.

FIG. 4 illustrates the tensile energy of Handsheet Samples 1 to 12.

FIG. 5 shows the breaking length of Handsheet Samples 7 to 12.

FIG. 6 illustrates the internal bond of Handsheet Samples 1 to 6.

EXPERIMENTS 1. Measuring Methods

In the following the measurement methods implemented in the examples aredescribed.

Particle Size Distribution (PSD) of the Employed Filler Materials BeforeStep a)

The particle size distribution of the products was measured using aMalvern Mastersizer 2000 Laser Diffraction System (Malvern InstrumentsPlc., Great Britain) using the Fraunhofer light scatteringapproximation. The method and instrument are known to the skilled personare commonly used to determine particle sizes of fillers and otherparticulate materials.

The measurement was carried out in an aqueous solution comprising 0.1wt.-% Na₄P₂O₇. The samples were dispersed using a high speed stirrer andin the presence of supersonics.

Particle Size Distribution (PSD) of the Filler Particles in SuspensionS1, S2 and SM

The particle size distribution of the products was measured using aMalvern Mastersizer 2000 Laser Diffraction System (Malvern InstrumentsPlc., Great Britain) using the Fraunhofer light scatteringapproximation. The method and instrument are known to the skilled personare commonly used to determine particle sizes of fillers and otherparticulate materials.

The measurement was carried out in an aqueous solution comprising 0.1wt.-% Na₄P₂O₇. The samples were dispersed using a high speed stirrer andin the absence of supersonics.

Full Width at Half Maximum Height (FWHM)

The particle size distribution data were displayed in an xy scatterdiagram and the data were arranged accordingly in x and y columnswhereas the size data were put in the x-column and the frequency datawas arranged in the y column. The maximum height (y_(m)) was determinedby sorting the particle size distribution curve by the frequency datapoints. The respective x-value was then defined as the peak position atthe maximum height (x_(m)). By dividing the maximum peak height by 2,the half maximal height was obtained (y_(m0.5)).

The four data points that have the closest y-value compared to the halfmaximum height value were defined, whereas, compared to the data pointof the half maximal height at the position of the maximal height P_(HM2)(x_(m)/y_(m0.5)):

P_(IL) was the data point having the nearest lower x- and the nearestlower y-value (x_(1L)/y_(1L)). P_(1H) was the data point having thenearest lower x- and the nearest higher y-value (x_(1H)/y_(1H)). P_(2L)was the data point having the nearest higher x- and the nearest lowery-value (x_(2L)/y_(2L)). P_(2H) was the data point having the nearesthigher x- and the nearest higher y-value (x_(2H)/y_(2H)).

The linearly interpolated x-positions (x_(1I) and x_(2I)) of the datapoints having the y-value of the half of maximal height value (y_(m2))were linearly interpolated as follows:

$x_{1I} = {x_{1\; L} + {\left( \frac{y_{{m0}{.5}} - y_{1\; L}}{y_{1H} - y_{1L}} \right)\left( {x_{1H} - x_{1\; L}} \right)}}$$x_{2I} = {x_{2\; H} + {\left( \frac{y_{2\; H} - y_{m\; 0.5}}{y_{2L} - y_{2\; H}} \right)\left( {x_{2\; L} - x_{2\; H}} \right)\mspace{14mu}{and}}}$F H M W = x_(2 I) − x_(1 I).Filler Content

The filler content in the handsheets was determined by burning a quarterof a dry handsheet in a muffle furnace heated to 570° C. After theburning was completed, the residue was transferred in a desiccator andallowed to cool down. When room temperature was reached, the weight ofthe residue was measured and the mass was related to the initiallymeasured weight of the dry quarter hand sheet.

Mechanical Strength Properties

Breaking length and tensile energy have been determined according to ENISO 1924-2 and the internal bond has been determined according to DIN54516.

2. Materials

Filler material 1 (P1): undispersed, scalenohedral precipitated calciumcarbonate (d₅₀=4.3 μm, measured with Malvern Mastersizer 2000),commercially available from Omya AG, Switzerland.

Filler material 2 (P2): Undispersed, aragonitic precipitated calciumcarbonate (d₅₀=4 μm, measured with Malvern Mastersizer 2000),commercially available from Omya AG, Switzerland.

Filler material 3 (P3): Selected, natural ground calcium carbonate(marble), dispersed product (Hydrocarb 60 ME), commercially availablefrom Omya AG, Switzerland. P3 is microcrystalline, has a rhombohedralparticle shape of high fineness, and was used as pre-dispersed slurryhaving a solids content of 78 wt.-%.

Filler material 4 (P4): Clay (Intramax 50, d₅₀=7 μm, measured byMastersizer 2000), powder form, commercially available from ImerysInternational Ltd, UK.

Flocculating additive 1 (FA1): Carboxymethyl cellulose (Finnfix 10,M_(W)=60000 g/mol, degree of substitution=0.8), commercially availablefrom CP Kelko, USA.

Flocculating additive 2 (FA2): Starch powder (C*Bond HR 35845),commercially available from Cargill, USA.

3. Examples Example 1—Preparation of Stock Solutions of FlocculatingAdditives

A stock solution of FA1 was prepared by adding FA1 into tap water at atemperature of 23° C. under stirring. Stirring was continued for 60minutes until FA1 had completely dissolved. FA1 was added in such anamount that a solution with a FA1 content of 4 wt.-%, based on the totalweight of the FA1 solution, was obtained.

A stock solution of FA2 was prepared by adding FA2 into deionized waterand heating the mixture for 30 minutes at 100° C. FA2 was added in suchan amount that a solution with a FA2 content of 1 wt.-%, based on thetotal weight of the FA2 solution, was obtained. The FA2 solution wascooled down to room temperature using a water bath and the amount ofwater lost by evaporation was added to readjust the solution to a FA2content of 1 wt.-%, based on the total weight of the FA2 solution.

Example 2—Preparation of Flocculated Filler Particles (InventiveExample)

A first aqueous suspension S1 was prepared by adding the amount of theFA1 stock solution indicated in Table 1 below to a solution of a firstfiller material under stirring at room temperature. The amount of FA1was chosen to obtain an overall FA1 content of 0.5 pph (parts perhundred on dry pigment) in the final aqueous suspension SM offlocculated filler particles.

A second aqueous suspension S2 was prepared by adding the amount of theFA2 stock solution indicated in Table 1 below to a solution of a secondfiller material under stirring at room temperature. The amount of FA2was chosen to obtain an overall FA2 content of 4.0 pph (parts perhundred on dry pigment) in the final aqueous suspension SM offlocculated filler particles. During the addition of the FA2 solutionflocculated filler particles formed.

The first aqueous suspension S1 and the second aqueous suspension S2were combined at room temperature in a separate vessel by pouring bothsuspensions simultaneously into the vessel under stirring, wherebyflocculated filler particles formed in the suspension. After completeaddition the resulting mixture was stirred for additional 5 minutes at ashear rate of 50 s⁻¹. Then the slurry was subjected for 15 minutes to aMegatron treatment for disaggregation of the flocs at a shear rate of 40000 s⁻¹ (Megatron MT 5000 with MTO 5000 Q working chamber, KinematicaAG, Luzern CH, circulation mode, 14 000 rpm).

The employed amounts and types of filler materials and the amounts ofthe employed flocculating additives are compiled in Table 1 below.

TABLE 1 Composition of prepared aqueous flocculated filler particlesuspensions. Ratio first filler First material/second Amount of Amountof filler Second filler filler material FA1 in S1 FA2 in S2 Samplematerial material dry/dry [wt.-%] [pph^(a)] [pph^(a)] 1 P3 P1 90/10 0.5640 2 P3 P1 10/90 5 4.4 3 P3 P1 50/50 1 8 4 P1 P3 50/50 1 8 5 P4 P3 50/501 8 6 P4 P1 50/50 1 8 7 P2 P1 10/90 5 4.4 8 P4 P3 70/30 0.7 13.3^(a)Parts per hundred based on dry filler material.

For every sample, the volume determined median particle size (d₅₀) ofthe flocculated filler particles, the particle size distribution thereofas well as the position of the main peak of the particle sizedistribution, main peak share i.e. the content of the area under themain peak in relation to the content of the sum of the area of allexisting peaks, the main peak height, the main peak half height, and theFWHM values were measured. The results are given in Table 2 below.

TABLE 2 Properties of flocculated filler particles. Main peak Main d₅₀position Main peak Main peak peak half FWHM Sample [μm] [μm] share [%]height [%] height [%] [μm] 1 21.8 22.9 96.4 8.0 4.0 40.7 2 8.3 10.0 91.710.0 5.0 12.8 3 13.5 15.1 93.9 9.2 4.6 22.9 4 11.9 13.2 93.6 9.7 4.819.4 5 14.7 17.4 100.0 8.1 4.1 28.6 6 11.2 13.2 100.0 8.7 4.3 19.8 7 7.88.7 90.5 9.8 4.9 12.2 8 10.2 11.2 100 10.4 5.2 15.3

FIG. 2 shows the particle size distributions of a first aqueoussuspension S1 including the filler material P1 and a second aqueoussuspension S2 including the filler material P5 (see sample 6, Table 1).It can be gathered from said figure that the flocculation that occurredin the second aqueous suspension S2 during the addition of flocculatingadditive FA2 resulted in an increased size of the filler particles. Theparticle size of P5 in the first aqueous suspension S1 did not change atall after addition of the flocculating additive FA1. After combining thefirst and second aqueous suspensions the flocculated filler particlesuspension obtained according to Example 2 (sample 6) had a FWMH of <20μm, which means that a very homogenous particle size distribution of thefirst and second filler material is obtained. Thus, Example 2 (sample 6)confirms that the process of the present invention allows to manufactureflocculated fillers having a homogenous and mono-modal particle sizedistribution in the meaning of the present invention.

Example 3—Preparation of Flocculated Filler Particles (ComparativeExample)

A first filler material and a second filler material indicated in Table3 below were mixed by adding the first filler material to the secondfiller material under stirring at room temperature. The resultingmixture FM was stirred for additional 5 minutes at a shear rate of 50s⁻¹. Then, the amount of FA1 stock solution indicated in Table 3 belowwas added to this mixture under stirring at room temperature. Theresulting mixture FM1 was stirred for additional 5 minutes at a shearrate of 50 s⁻¹. Then, the amount of FA2 stock solution indicated inTable 3 below was added to this mixture under stirring at roomtemperature, whereby flocculated filler particles formed in suspension.After complete addition, the resulting mixture was stirred foradditional 5 minutes at a shear rate of 50 s⁻¹. Then the slurry wassubjected for 15 minutes to a Megatron treatment for disaggregation ofthe flocs at a shear rate of 40 000 s⁻¹ (Megatron MT 5000 with MTO 5000Q working chamber, Kinematica AG, Luzern CH, circulation mode, 14 000rpm).

TABLE 3 Composition of prepared aqueous flocculated filler particlesuspensions. Amount Ratio first filler of First material/second FA1 inAmount of filler Second filler filler material FM FA2 in FM Samplematerial material dry/dry [wt.-%] [pph^(a)] [pph^(a)] 9 P3 P1 10/90 0.54 10 P4 P3 70/30 0.5 4 ^(a)Parts per hundred based on dry fillermaterial.

Example 4—Preparation and Testing of Handsheets

60 g (dry) pulp were diluted in 10 dm³ tap water, and then the filler tobe tested was added in an amount so as to obtain the overall fillercontent based on the final paper weight. The suspension was stirred for30 minutes. Subsequently, 0.06% (based on dry weight) of apolyacrylamide (Polymin 1530, commercially available from BASF, Germany)was added as a retention aid and sheets of 80 g/m² were formed using theRapid-Köthen hand sheet former. Each sheet was dried using theRapid-Köthen drier. The composition of the handsheets is given in Table4 below.

TABLE 4 Composition of handsheets. Flocculated FM of Flocculated fillerof Flocculated Flocculated FM of Example filler of Example filler offiller of Example 3- Example 3- Example Example Hand- 3- Sample 3-Sample 2- 2- sheet Pulp Sample 9 10 Sample 9 10 Sample 2 Sample 8 Sample[wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] [wt.-%] 1 (c) 80 — 20 —— — — 2 (c) 75 — 25 — — — — 3 (c) 80 — — — 20 — — 4 (c) 75 — — — 25 — —5 (i) 80 — — — — — 20 6 (i) 75 — — — — — 25 7 (c) 80 20 — — — — — 8 (c)75 25 — — — — — 9 (c) 80 — — 20 — — — 10 (c)  75 — — 25 — — — 11 (i)  80— — — — 20 — 12 (i)  75 — — — — 25 — (i) = inventive; (c) = comparative.

The mechanical properties of the prepared Handsheet Samples 1 to 12 weretested, in particular the tensile energy, the breaking length and theinternal bond have been determined. The results are shown in FIGS. 4, 5and 6.

As can be gathered from FIG. 4, the flocculation of the filler particlemixture (Example 3) leads to an increased tensile energy in hand sheets(compare Handsheet Sample 3 to 1, 4 to 2, 9 to 7 and 10 to 8). However,if the flocculation is done according to the present invention (Example2), the tensile energy increases even further (compare Handsheet Sample5 to 3, 6 to 4, 11 to 9 and 12 to 10).

FIG. 5 reveals also that the breaking length of hand sheets containingflocculated filler mixtures (Handsheet Sample 9 and 10) is increasedcompared to the filler mixture alone (compare Handsheet Sample 9 to 7and 10 to 8). An even higher increase in breaking length can be seen forflocculated filler containing hand sheets where the filler mixture wasflocculated according to the present invention (compare Handsheet Sample11 to 9 and 12 to 10).

The flocculation of particle filler mixtures also increases the internalbond of hand sheets containing such fillers, compared to hand sheetscontaining the filler mixtures alone as can be seen in FIG. 6 (compareHandsheet Sample 3 to 1 and 4 to 2). When the filler is flocculatedaccording to the present invention, the internal bond of hand sheetscontaining such flocculated filler is increased even more (compareHandsheet Sample 5 to 3 and 6 to 4).

The invention claimed is:
 1. A process for the preparation offlocculated filler particles comprising: providing at least one firstaqueous suspension S1 in a first vessel that comprises at least oneflocculating additive A and at least one first filler material;providing at least one second aqueous suspension S2 in a second vesselthat comprises at least one flocculating additive B and at least onesecond filler material, wherein the at least one flocculating additive Bis different from the at least one flocculating additive A, wherein theat least one first filler material in the first aqueous suspension S1and the at least one second filler material in the second aqueoussuspension S2 are different; and combining the at least one firstaqueous suspension S1 with the at least one second aqueous suspension S2simultaneously in a third vessel, under conditions effective to form amixture, the mixture comprising an aqueous suspension SM of flocculatedfiller particles.
 2. The process according to claim 1, wherein aBrookfield viscosity of the first aqueous suspension S1 and/or thesecond aqueous suspension S2 and/or the aqueous suspension SM is lessthan 5,000 mPa·s at 25° C.
 3. The process according to claim 1, whereina Brookfield viscosity of the first aqueous suspension S1 and/or thesecond aqueous suspension S2 and/or the aqueous suspension SM is lessthan 1,000 mPa·s at 25° C.
 4. The process according to claim 1, whereina Brookfield viscosity of the first aqueous suspension S1 and/or thesecond aqueous suspension S2 and/or the aqueous suspension SM is between10 and 200 mPa·s at 25° C.
 5. The process according to claim 1, whereinthe at least one flocculating additive A is a cationic polymer selectedfrom the group consisting of cationic starch, polyamines,polyethyleneimines, polyacrylamides, cationic amine amide,epichlorohydrin resins, polydiallyldimethylammonium chloride, cationicguar, and any mixture thereof.
 6. The process according to claim 1,wherein the at least one flocculating additive A is a cationic starch.7. The process according to claim 1, wherein the at least oneflocculating additive B is an anionic polymer selected from the groupconsisting of carboxymethyl cellulose, anionic starch, anionic guar,anionic xanthan gum, and any mixture thereof.
 8. The process accordingto claim 1, wherein the at least one flocculating additive B is ananionic carboxymethyl cellulose.
 9. The process according to claim 8,wherein the at least one flocculating additive A is a cationic starch.10. The process according to claim 9, wherein the at least one firstfiller material in the first suspension S1 is ground calcium carbonateand the at least one second filler material in the second suspension S2is precipitated calcium carbonate.
 11. The process according to claim 1,wherein the aqueous suspension SM is sheared during and/or aftersimultaneous combination of the at least two aqueous suspensions. 12.The process according to claim 1, wherein the aqueous suspension SM issheared in at least two steps at different shear rates.
 13. The processaccording to claim 1, wherein the aqueous suspension SM is sheared in atleast two steps at different shear rates, wherein the first shear rateis lower than the second shear rate.
 14. The process according to claim1, wherein the at least one first filler material and the at least onesecond filler material are selected from the group consisting of acalcium carbonate-comprising material, ground calcium carbonate,precipitated calcium carbonate, modified calcium carbonate, talc, clay,dolomite, marble, titanium dioxide, kaolin, silica, alumina, mica,aluminium trihydrate, magnesium hydroxide, plastic pigments, a hybridmaterial comprising an organic filler and an inorganic chemicalcomposition, and any mixture thereof.
 15. The process according to claim1, wherein the at least one first filler material in the firstsuspension S1 is ground calcium carbonate and the at least one secondfiller material in the second suspension S2 is precipitated calciumcarbonate and/or clay.
 16. The process according to claim 1, wherein theat least one first filler material in the first suspension S1 is groundcalcium carbonate and the at least one second filler material in thesecond suspension S2 is precipitated calcium carbonate.
 17. The processaccording to claim 1, wherein the content of the at least oneflocculating additive A in the first aqueous suspension S1 is from 0.5to 10 wt.-%, based on the total weight of the first aqueous suspensionS1, and/or the content of the at least one flocculating additive B inthe second aqueous suspension S2 is from 0.1 to 10 wt.-%, based on thetotal weight of the second aqueous suspension S2.
 18. The processaccording to claim 1, wherein the content of the at least oneflocculating additive A in the first aqueous suspension S1 is from 3 to5 wt.-%, based on the total weight of the first aqueous suspension S1,and/or the content of the at least one flocculating additive B in thesecond aqueous suspension S2 is from 0.2 to 0.8 wt.-%, based on thetotal weight of the second aqueous suspension S2.
 19. The processaccording to claim 1, wherein the content of the at least one firstfiller material in the first aqueous suspension S1 is from 15 to 65wt.-%, based on the total weight of the first aqueous suspension S1, andthe content of the at least one second filler material in the secondaqueous suspension S2 is from 15 to 65 wt.-%, based on the total weightof the second aqueous suspension S2.
 20. The process according to claim1, wherein the content of the at least one first filler material in thefirst aqueous suspension S1 is from 10 to 40 wt.-%, based on the totalweight of the first aqueous suspension S1, and the content of the atleast one second filler material in the second aqueous suspension S2 isfrom 10 to 40 wt.-%, based on the total weight of the second aqueoussuspension S2.
 21. The process according to claim 1, wherein the massratio of the at least one first filler material in the first aqueoussuspension and the at least one second filler material in the secondaqueous suspension S1:S2 is between 99:1 and 1:99.
 22. The processaccording to claim 1, wherein the mass ratio of the at least one firstfiller material in the first aqueous suspension and the at least onesecond filler material in the second aqueous suspension S1:S2 is between95:15 and 5:85.
 23. The process according to claim 1, wherein the massratio of the at least one first filler material in the first aqueoussuspension and the at least one second filler material in the secondaqueous suspension S1:S2 is between 70:30 and 30:70.
 24. The processaccording to claim 1, wherein the aqueous suspension SM has a solidscontent of from 1 to 75 wt.-%, based on the total weight of the aqueoussuspension SM.
 25. The process according to claim 1, wherein the aqueoussuspension SM has a solids content of from 2 to 60 wt.-%, based on thetotal weight of the aqueous suspension SM.
 26. The process according toclaim 1, wherein the aqueous suspension SM has a solids content of from5 to 35 wt.-%, based on the total weight of the aqueous suspension SM.27. The process according to claim 1, wherein the aqueous suspension SMof flocculated filler particles has a mono-modal particle sizedistribution.
 28. The process according to claim 1, wherein the aqueoussuspension SM of flocculated filler particles has a volume definedparticle size polydispersity expressed as full width at half maximumheight (FWHM) of less than 45 μm.
 29. The process according to claim 1,wherein the aqueous suspension SM of flocculated filler particles has avolume defined particle size polydispersity expressed as full width athalf maximum height (FWHM) of less than 30 μm.
 30. The process accordingto claim 1, wherein the aqueous suspension SM of flocculated fillerparticles has a volume defined particle size polydispersity expressed asfull width at half maximum height (FWHM) of less than 10 μm.
 31. Theprocess according to claim 1, wherein a content of the at least onefirst filler material in the first aqueous suspension S1 is from 1 to 85wt.-%, based on a total weight of the first aqueous suspension S1. 32.The process according to claim 1, wherein a content of the at least onesecond filler material in the second aqueous suspension S2 is from 1 to85 wt.-%, based on a total weight of the second aqueous suspension S2.